Network communications systems and methods

ABSTRACT

Methods, systems, and devices for network communications to reduce optical beat interference (OBI) in upstream communications are described. For example, a fiber node may provide a seed source to injection lock upstream laser diodes. Therefore, upstream communications from each injection locked laser diode may primarily include the wavelength associated with each seed source. The seed sources may be unique to each end device and configured to minimize OBI. That is, the upstream laser diodes may be generic, but the collected seed source may enable upstream communications at varying wavelengths. The end device may provide upstream communications by externally modulating a signal generated by the injection locked laser diode.

CROSS REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of and priority to U.S. patentapplication Ser. No. 15/861,303 filed Jan. 3, 2018, which claims benefitof and priority to U.S. patent application Ser. No. 15/283,632 filedOct. 3, 2016, which claims the benefit of and priority to U.S.Provisional Patent Application Ser. No. 62/321,211, filed Apr. 12, 2016,each of which are incorporated herein by reference in their entireties,and additionally claims the benefit of and priority to U.S. ProvisionalPatent Application Ser. No. 62/625,096, all of which are incorporatedherein by reference in its entirety.

BACKGROUND

The field of the disclosure relates generally to fiber communicationnetworks, and more particularly, to optical networks utilizingsimultaneous upstream communications.

Telecommunication networks include an access network through which enddevice subscribers connect to a service provider. Bandwidth requirementsfor delivering high-speed data and video services through the accessnetwork are rapidly increasing to meet growing consumer demands. Atpresent, data delivery over the access network is growing by gigabits(Gb)/second for residential subscribers, and by multi-Gb/s for businesssubscribers. Present access networks are based on passive opticalnetwork (PON) access technologies, which have become the dominant systemarchitecture to meet the growing high capacity demand from end devices.

Gigabit PON and Ethernet PON (EPON) architectures presently provideabout 2.5 Gb/s data rates for downstream transmission and 1.25 Gb/s forupstream transmission (half of the downstream rate). 10 Gb/s PONs(XG-PON or IEEE 10G-EPON) have begun to be implemented forhigh-bandwidth applications, and a 40 Gb/s PON scheme, which is based ontime and wavelength division multiplexing (TWDM and WDM) has recentlybeen standardized. A growing need therefore exists to develophigher/faster data rates per-subscriber to meet future bandwidth demand,and also increase the coverage for services and applications, but whilealso minimizing the capital and operational expenditures necessary todeliver higher capacity and performance access networks.

One known solution to increase the capacity of a PON is the use of WDMtechnology to send a dedicated wavelength signal to end devices. Currentdetection scheme WDM technology, however, is limited by its low receiversensitivity when coherent signals are employed, and also by the fewoptions available to upgrade and scale the technology, particularly withregard to use in conjunction with the lower-quality legacy fiberenvironment. The legacy fiber environment requires operators to squeezemore capacity out of the existing fiber infrastructure to avoid costsassociated with having to retrench new fiber installment. Conventionalcable access networks typically include six fibers per node, servicingas many as 500 end devices, such as home subscribers. Conventional nodescannot be split further without adding fiber and do not typicallycontain spare (unused) fibers, and thus there is a need to utilize thelimited fiber availability in a more efficient and cost-effectivemanner.

Coherent technology has been proposed as one solution to increase bothreceiver sensitivity and overall capacity for WDM-PON optical accessnetworks, in both brown and green field deployments. Coherent technologyoffers superior receiver sensitivity and extended power budget, and highfrequency selectivity that provides closely-spaced dense or ultra-denseWDM without the need for narrow band optical filters. Moreover, amulti-dimensional recovered signal experienced by coherent technologyprovides additional benefits to compensate for linear transmissionimpairments such as chromatic dispersion (CD) and polarization-modedispersion (PMD), and to efficiently utilize spectral resources tobenefit future network upgrades through the use of multi-level advancedmodulation formats. Long distance transmission using coherenttechnology, however, requires elaborate post-processing, includingsignal equalizations and carrier recovery, to adjust for impairmentsexperienced along the transmission pathway, thereby presentingsignificant challenges by significantly increasing system complexity.

Coherent technology in long-haul optical systems typically requiressignificant use of high quality discrete photonic and electroniccomponents, such as digital-to-analog converters (DAC), analog todigital converters (ADC), and digital signal processing (DSP) circuitrysuch as an application-specific integrated circuit (ASIC) utilizingcomplimentary metal-oxide semiconductor (CMOS) technology, to compensatefor noise, frequency drift, and other factors affecting the transmittedchannel signals over the long distance optical transmission. Coherentpluggable modules for metro solution have gone through C Form-factorpluggable (CFP) to CFP2 and future CFP4 via multi-source agreement (MSA)standardization to reduce their footprint, to lower costs, and also tolower power dissipation. However, these modules still requiresignificant engineering complexity, expense, size, and power to operate,and therefore have not been practical to implement in accessapplications.

There could be many services that coexist in cable's optical accessnetworks such as the traditional subcarrier multiplexed analog video,digital video and DOC SIS data services along with the less common radiofrequency over glass (RFOG), EPON, Point-to-Point digital fiber linksand others. When these are aggregated together, or even worse when theyare aggregated over fiber with RFOG and analog, optical beatinterference (OBI) becomes a significant problem. There is a need for asystem that provides services that coexist in cable's optical accessnetworks, meets a bandwidth demand, and decreases problems associatedwith OBI.

SUMMARY

Simultaneous transmissions and transmissions from different services mayresult in optical beat interference (OBI). For example, if two devicestransmit using wavelengths close enough to one another in frequency suchthat the difference falls within the frequency response of the opticalreceiver, the transmissions may cause OBI. The system may ensure thatupstream transmissions are maintained according to certain wavelengthwindows in order to decrease OBI. For example, a fiber node may providemore than one seed source (e.g., a narrow wavelength band) and transmiteach seed source to an end device. The seed sources may be maintainedwithin constraints of wavelength filter windows such that the wavelengthbands of each of the seed sources minimize OBI between signalscorresponding to the wavelength bands. The end devices may use injectionlocking of upstream laser diodes to generate upstream communicationsaccording to the collected wavelength band, thus minimizing OBIresulting in simultaneous upstream communications from the devices. Theend devices may further use external modulation of the laser diodes toencode the signals generated by the laser diodes for upstreamcommunications.

A method of network communications is described. The method may includean optical circulator configured to collect a seed source spanning awavelength range and direct the seed source to a laser diode, the laserdiode configured to output a signal including primarily the wavelengthrange based on the collecting the seed source at the laser diode, and anexternal modulator configured to modulate the signal output by the laserdiode, where the optical circulator is further configured to collect themodulated signal and direct the modulated signal upstream.

An apparatus for network communications is described. The apparatus mayinclude a processor, memory in electronic communication with theprocessor, and instructions stored in the memory. The instructions maybe executable by the processor to cause the apparatus to an opticalcirculator configured to collect a seed source spanning a wavelengthrange and direct the seed source to a laser diode, the laser diodeconfigured to output a signal including primarily the wavelength rangebased on the collecting the seed source at the laser diode, and anexternal modulator configured to modulate the signal output by the laserdiode, where the optical circulator is further configured to collect themodulated signal and direct the modulated signal upstream.

Another apparatus for network communications is described. The apparatusmay include means for an optical circulator configured to collect a seedsource spanning a wavelength range and direct the seed source to a laserdiode, the laser diode configured to output a signal including primarilythe wavelength range based on the collecting the seed source at thelaser diode, and an external modulator configured to modulate the signaloutput by the laser diode, where the optical circulator is furtherconfigured to collect the modulated signal and direct the modulatedsignal upstream.

A non-transitory computer-readable medium storing code for networkcommunications is described. The code may include instructionsexecutable by a processor to an optical circulator configured to collecta seed source spanning a wavelength range and direct the seed source toa laser diode, the laser diode configured to output a signal includingprimarily the wavelength range based on the collecting the seed sourceat the laser diode, and an external modulator configured to modulate thesignal output by the laser diode, where the optical circulator isfurther configured to collect the modulated signal and direct themodulated signal upstream.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, a filter configured to,separate the seed source and the downstream signal, and direct the seedsource to the optical circulator and the downstream signal to aphotodetector.

Some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein may further includeoperations, features, means, or instructions for outputting the signalincluding primarily the wavelength range may be based on injectionlocking the laser diode using the seed source.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, a second optical circulatordisposed between the laser diode and the external modulator.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the second optical circulatormay be in one-way communication with the external modulator and intwo-way communication with the laser diode.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the laser diode further mayinclude operations, features, means, or instructions for a front facetand the laser diode may be further configured to collect the seed sourceat the front facet of the laser diode.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, a second optical circulatordisposed between and in one-way communication with the opticalcirculator and the laser diode.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the laser diode further mayinclude operations, features, means, or instructions for a rear facetand the laser diode may be configured to collect the seed source by therear facet of the laser diode.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, a photodetector in one-waycommunication with the second optical circulator and configured tocollect a portion of the seed source reflected from the rear facet ofthe laser diode to the photodetector, by the second optical circulator.

A method of network communications is described. The method may includean optical circulator configured to collect a combined signal includinga downstream signal and a seed source spanning a wavelength range, afilter configured to collect the combined signal from the opticalcirculator and separate the downstream signal and the seed source, alaser diode configured to collect the seed source and output a signalincluding primarily the wavelength range based on collecting the seedsource at the laser diode, and an external modulator configured tomodulate the laser diode signal output, where the optical circulator isfurther configured to collect the modulated signal from the externalmodulator and direct the modulated signal upstream.

An apparatus for network communications is described. The apparatus mayinclude a processor, memory in electronic communication with theprocessor, and instructions stored in the memory. The instructions maybe executable by the processor to cause the apparatus to an opticalcirculator configured to collect a combined signal including adownstream signal and a seed source spanning a wavelength range, afilter configured to collect the combined signal from the opticalcirculator and separate the downstream signal and the seed source, alaser diode configured to collect the seed source and output a signalincluding primarily the wavelength range based on collecting the seedsource at the laser diode, and an external modulator configured tomodulate the laser diode signal output, where the optical circulator isfurther configured to collect the modulated signal from the externalmodulator and direct the modulated signal upstream.

Another apparatus for network communications is described. The apparatusmay include means for an optical circulator configured to collect acombined signal including a downstream signal and a seed source spanninga wavelength range, a filter configured to collect the combined signalfrom the optical circulator and separate the downstream signal and theseed source, a laser diode configured to collect the seed source andoutput a signal including primarily the wavelength range based oncollecting the seed source at the laser diode, and an external modulatorconfigured to modulate the laser diode signal output, where the opticalcirculator is further configured to collect the modulated signal fromthe external modulator and direct the modulated signal upstream.

A non-transitory computer-readable medium storing code for networkcommunications is described. The code may include instructionsexecutable by a processor to an optical circulator configured to collecta combined signal including a downstream signal and a seed sourcespanning a wavelength range, a filter configured to collect the combinedsignal from the optical circulator and separate the downstream signaland the seed source, a laser diode configured to collect the seed sourceand output a signal including primarily the wavelength range based oncollecting the seed source at the laser diode, and an external modulatorconfigured to modulate the laser diode signal output, where the opticalcirculator is further configured to collect the modulated signal fromthe external modulator and direct the modulated signal upstream.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, a second optical circulatordisposed between the laser diode and the external modulator andconfigured to collect the seed source from the filter, where the secondoptical circulator may be in one-way communication with the filter andthe external modulator and in two-way communication with the laserdiode.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, a second external modulatordisposed between the optical circulator and the second opticalcirculator, where the second external modulator may be configured tocollect the laser diode signal output from the second optical circulatorand further configured to direct a second externally modulated signal tothe optical circulator, and a phase shift element disposed between theexternal modulator and the second optical circulator.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the seed source may be acoherent signal.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, a polarization beam splitterdisposed between the second optical circulator and the phase shiftelement.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, a third external modulatordisposed between the polarization beam splitter and the opticalcirculator, where the third external modulator may be configured toinput a polarized signal from the polarization beam splitter, a fourthexternal modulator, and a second phase shift element disposed betweenthe polarization beam splitter and the fourth external modulator, wherethe fourth external modulator may be configured to input the phaseshifted signal from the second phase shift element.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, a polarization combinerdisposed between the optical circulator and the external modulator.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the external modulator may beconfigured to use coherent modulation such that the modulated signalincludes more than one data stream.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the external modulatorfurther includes an in-phase quadrature modulator.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the laser diode may beconfigured to collect any seed source of a set of seed sources eachspanning a unique wavelength range.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the filter may be furtherconfigured to direct the downstream signal to a photodetector.

A method of network communications is described. The method may includecollecting, at an optical circulator, a seed source spanning awavelength range, generating a signal including primarily the wavelengthrange based on collecting the seed source, externally modulating thesignal including primarily the wavelength range, and outputting, by theoptical circulator, the modulated signal.

An apparatus for network communications is described. The apparatus mayinclude a processor, memory in electronic communication with theprocessor, and instructions stored in the memory. The instructions maybe executable by the processor to cause the apparatus to collect, at anoptical circulator, a seed source spanning a wavelength range, generatea signal including primarily the wavelength range based on collectingthe seed source, externally modulate the signal including primarily thewavelength range, and output, by the optical circulator, the modulatedsignal.

Another apparatus for network communications is described. The apparatusmay include means for collecting, at an optical circulator, a seedsource spanning a wavelength range, generating a signal includingprimarily the wavelength range based on collecting the seed source,externally modulating the signal including primarily the wavelengthrange, and outputting, by the optical circulator, the modulated signal.

A non-transitory computer-readable medium storing code for networkcommunications is described. The code may include instructionsexecutable by a processor to collect, at an optical circulator, a seedsource spanning a wavelength range, generate a signal includingprimarily the wavelength range based on collecting the seed source,externally modulate the signal including primarily the wavelength range,and output, by the optical circulator, the modulated signal.

Some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein may further includeoperations, features, means, or instructions for generating the signalfurther includes injection locking the laser diode using the seedsource.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, generating the signal furthermay include operations, features, means, or instructions for driving thelaser diode at a constant current.

Some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein may further includeoperations, features, means, or instructions for externally modulatingthe signal includes modulating the signal based on one or more datastreams.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a fiber communication system inaccordance with an embodiment of the present disclosure.

FIGS. 2 through 5 are schematic illustrations depicting a transmitterthat can be utilized with the fiber communication system depicted inFIG. 1.

FIG. 6 is a schematic illustration depicting an upstream connection thatcan be utilized with the fiber communication system depicted in FIG. 1.

FIG. 7 is a schematic illustration depicting a processing architectureimplemented with the fiber communication system depicted in FIG. 1.

FIG. 8 is a flow chart diagram of a downstream optical network process.

FIG. 9 is a flow chart diagram of an upstream optical network processthat can be implemented with the downstream process depicted in FIG. 8.

FIGS. 10 through 12 are schematic illustrations of fiber communicationsystems in accordance with aspects of the present disclosure.

FIGS. 13A-13C are schematic illustrations of fiber communication systemsin accordance with aspects of the present disclosure.

FIGS. 14A-14B are schematic illustrations of fiber communication systemsin accordance with aspects of the present disclosure.

FIG. 15 is a process flow in accordance with aspects of the presentdisclosure.

FIG. 16 is a block diagram of a fiber node in accordance with aspects ofthe present disclosure.

FIG. 17 is a block diagram of an end device in accordance with aspectsof the present disclosure.

FIGS. 18 through 22 are flow chart diagrams illustrating a method inaccordance with aspects of the present disclosure.

DETAILED DESCRIPTION

An architecture to minimize optical beat interference (OBI) isdescribed. The architecture may enable multiple transmissions (e.g.,upstream transmissions from one or more end devices) at the same time.For example, a system may be a radio frequency over glass (RFOG) system.Certain types of RFOG systems (e.g., RFOG systems carrying data overcable service interface specification (DOCSIS) 3.1 and earlier versions)may include multiple DOCSIS media access control (MAC) layer domainswithin an optical mode serving area (e.g., an area served by thesystem), which may enable simultaneous upstream transmissions. Here,multiple simultaneous transmissions may be allowed in synchronous codedivision multiple access (S-CDMA) mode on the same channel and also inDOCSIS 3.0 and earlier modes across multiple channels. That is, theremay be a first transmission on a first channel at the same time thatanother device transmits on other channels. In DOCSIS 3.1 there may alsobe multiple simultaneous transmission that are scheduled within the sameupstream channel.

Additionally or alternatively, the system may enable transmissionscorresponding to different services (e.g., RFOG, ethernet passiveoptical network (EPON), etc.). Even though EPON does not utilizesimultaneous transmissions, coexistence issues when deployed along withother technologies may arise. The approach proposed here may enable EPONsystems and other systems coexist in the same optical network.

Simultaneous transmissions and transmissions from different services mayresult in OBI. For example, if two devices transmit using wavelengthsclose enough in frequency such that their difference falls within thefrequency response of the optical receiver, their transmissions maycause OBI. The system may ensure that upstream transmissions aremaintained according to certain wavelength windows. For example, a fibernode may provide more than one narrow wavelength band (e.g., a seedsource) and transmit each seed source to an end device. The seed sourcesmay be maintained within constraints of wavelength filter windows suchthat the wavelength bands of each of the seed sources minimize OBIbetween signals corresponding to the wavelength bands. The end devicesmay use injection locking of upstream laser diodes to generate upstreamcommunications according to the collected wavelength band, thusminimizing OBI resulting in simultaneous upstream communications fromthe devices. The end devices may alternatively use injection locking ofa reflective semiconductor optical amplifier (RSOA) or alternatively usea semiconductors optical amplifier.

The system may multiplex and aggregate services over fiber accessnetworks of cable and other. The approach allows to dedicate awavelength per end-device without causing OBI regardless of thecombination of services desired. The dedicated wavelengths can includeintensity modulated optical links, coherent optical links, or acombination of both. The end devices may support dense wavelengthdivision multiplexing (DWDM), but may not use wavelength specificstructures.

A number of terms may be referenced herein and may be interpreted as setforth below.

The singular forms “a,” “an,” and “the” include plural references unlessthe context clearly dictates otherwise.

“Optional” or “optionally” may indicate that the subsequently describedevent or circumstance may or may not occur, and that the descriptionincludes instances where the event occurs and instances where it doesnot.

Approximating language, as used herein throughout the specification andclaims, may be applied to modify any quantitative representation thatcould permissibly vary without resulting in a change in the basicfunction to which it is related. Accordingly, a value modified by a termor terms, such as “about,” “approximately,” and “substantially,” are notto be limited to the precise value specified. In at least someinstances, the approximating language may correspond to the precision ofan instrument for measuring the value. Here and throughout thespecification and claims, range limitations may be combined and/orinterchanged; such ranges are identified and include all the sub-rangescontained therein unless context or language indicates otherwise.

Aspects of the disclosure are initially described in the context offiber communications systems. Aspects of the disclosure are furtherillustrated by and described with reference to process flows, blockdiagrams, and flowcharts that relate to network communications systemsand methods.

FIG. 1 is a schematic illustration of a fiber communication system 100in accordance with an embodiment of the present disclosure. System 100includes an optical hub 102, a fiber node 104, and an end device 106.Optical hub 102 is, for example, a central office, a communications hub,or an optical line terminal (OLT). In the embodiment shown, fiber node104 is illustrated for use with a passive optical network (PON). Enddevice 106 is a downstream termination unit, which can represent, forexample, a customer device, customer premises (e.g., an apartmentbuilding), a business user, or an optical network unit (ONU). In anembodiment, system 100 utilizes a coherent Dense Wavelength DivisionMultiplexing (DWDM) PON architecture.

Optical hub 102 communicates with fiber node 104 by way of downstreamfiber 108. Optionally, where upstream communication is desired alongsystem 100, optical hub 102 further connects with fiber node 104 by wayof upstream fiber 110. In operation, downstream fiber 108 and upstreamfiber 110 are typically 30 km or shorter. However, according to theembodiments presented herein, greater lengths are contemplated, such asbetween 100 km and 1000 km. In an embodiment, fiber node 104 connectswith end device 106 by way of fiber optics 112. Alternatively, fibernode 104 and end device 106 may be integrated as a single device, whichmay be located at a customer premises or at the fiber node 104 if nodemanagement capabilities are intended through an end device 106. Wherefiber node 104 and end device 106 are separate devices, fiber optics 112typically spans a distance of approximately 5000 feet or less. In somecases, fiber optics 112 may include two cascading fiber nodes 104 wherethe fiber optics 112 may span distances greater than 5000 feet.

Optical hub 102 includes an optical frequency comb generator 114, whichmay be configured to receive a high quality source signal 116 from anexternal laser 118 and thereby generate multiple coherent tones 120(1),120(1′), . . . 120(N), 120(N′). Optical frequency comb generator 114utilizes, for example, a mode-locked laser, a gain-switched laser, orelectro-optic modulation, and is constructed such that multiple coherenttones 120 are generated as simultaneous low-linewidth wavelengthchannels of known and controllable spacing. Alternatively (e.g., tooptical frequency comb generator 114), multiple high quality lasersources may be tuned to wavelengths that are spaced apart to generatethe multiple coherent tones 120(1), 120(1′), . . . 120(N), 120(N′). Thisadvantageous aspect of the upstream input signal into system 100 allowsa simplified architecture throughout the entire downstream portion ofsystem 100, as described further below.

Generated coherent tones 120 are fed into an amplifier 122, and theamplified signal therefrom is input into a first hub opticaldemultiplexer 124. In an embodiment, amplifier 122 is an erbium-dopedfiber amplifier (EDFA). Optical hub 102 further includes a downstreamtransmitter 126 and a hub optical multiplexer 128. In an embodiment,optical hub 102 optionally includes a hub optical splitter 130, anupstream receiver 132, and a second hub optical demultiplexer 134.

Downstream transmitter 126 includes a downstream optical circulator 136and a downstream modulator 138. In an embodiment, downstream modulator138 is an injection locked laser modulator. Upstream receiver 132includes an upstream integrated coherent receiver (ICR) 140, an upstreamanalog to digital converter (ADC) 142, and an upstream digital signalprocessor (DSP) 144. In the embodiment, fiber node 104 includes a nodeoptical demultiplexer 146. In an alternative embodiment, where upstreamtransmission is desired, fiber node 104 further includes a node opticalmultiplexer 148. In the embodiment, node optical demultiplexer 146 andnode optical multiplexer 148 are passive devices.

End device 106 further includes a downstream receiver 150. In anembodiment, downstream receiver 150 has a similar architecture toupstream receiver 132, and includes a downstream ICR 152, a downstreamADC 154, and a downstream DSP 156. For upstream transmission, end device106 optionally includes end device optical splitter 158, which may belocated within downstream receiver 150 or separately, and an upstreamtransmitter 160. In an embodiment, upstream transmitter 160 has asimilar architecture to downstream transmitter 126, and includes anupstream optical circulator 162, and an upstream modulator 164.

In operation, system 100 utilizes optical frequency comb generator 114and amplifier 122 convert the input high quality source signal 116 intomultiple coherent tones 120 (e.g., 32 tones, 64 tones, etc.), which arethen input to first hub optical demultiplexer 124. In an embodiment,high quality source signal 116 is of sufficient amplitude and a narrowbandwidth such that a selected longitudinal mode of signal 116 istransmitted into optical frequency comb generator 114 without adjacentlongitudinal modes, which are suppressed prior to processing by combgenerator 114. First hub optical demultiplexer 124 then outputs aplurality of phase synchronized coherent tone pairs 166(1), 166(2), . .. 166(N). That is, the generated coherent frequency tones 120 areamplified by amplifier 122 to enhance optical power, and thendemultiplexed into multiple separate individual phased synchronizedcoherent tone source pairs 166. For simplicity of discussion, thefollowing description pertains only to coherent tone pair 166(1)corresponding to the synchronized pair signal for the first channeloutput, which includes a first unmodulated signal 168 for Ch1 and asecond unmodulated signal 170 for Ch1′, and their routing through system100.

With source signal 116 of a high quality, narrow band, and substantiallywithin a single longitudinal mode, coherent tone pair 166(1), includingfirst unmodulated signal 168 (Ch1) and second unmodulated signal 170(Ch1′), is output as a high quality, narrowband signal, which thenserves as both a source of seed and local oscillator (LO) signals forboth downstream and upstream transmission and reception directions ofsystem 100. That is, by a configuration, the architecture of opticalfrequency comb generator 114 advantageously produces high qualitycontinuous wave (CW) signals. Specifically, first unmodulated signal 168(Ch1) may function as a downstream seed and upstream LO throughoutsystem 100, while second unmodulated signal 170 (Ch1′) concurrently mayfunction as an upstream seed and downstream LO for system 100.

According to the embodiment, within optical hub 102, first unmodulatedsignal 168 (Ch1) is divided by hub optical splitter 130 and isseparately input to both downstream transmitter 126 and upstreamreceiver 132 as a “pure” signal, and i.e., substantially low amplitude,narrow bandwidth continuous wave does not include adhered data. Firstunmodulated signal 168 (Ch1) thus becomes a seed signal for downstreamtransmitter 126 and an LO signal for upstream receiver 132. In anembodiment, within downstream transmitter 126, first unmodulated signal168 (Ch1) passes through downstream optical circulator 136 intodownstream modulator 138, in which one or more laser diodes (not shownin FIG. 1, described below with respect to FIGS. 2-5) are excited, andadhere data (also not shown in FIG. 1, described below with respect toFIGS. 2-5) to the signal that then exits downstream optical circulator136 as downstream modulated data stream 172 (Ch1).

In an embodiment, downstream optical circulator 136 is within downstreamtransmitter 126. Alternatively, downstream optical circulator 136 may bephysically located separately from downstream transmitter 126, or elsewithin the confines of downstream modulator 138. Downstream modulateddata stream 172 (Ch1) is then combined in hub optical multiplexer 128with the plurality of modulated/unmodulated data stream pairs from otherchannels (not shown) and transmitted over downstream fiber 108, to anode optical demultiplexer 174 in fiber node 104, which then separatesthe different channel stream pairs for transmission to differentrespective end devices 106. At end device 106, because the data streampair 170, 172 entering downstream receiver 150 is a phase synchronized,digital signal processing at downstream DSP 156 is greatly simplified,as described below with respect to FIG. 7.

Where upstream reception is optionally sought at optical hub 102, secondunmodulated signal 170 (Ch1′) is divided, within end device 106, by enddevice optical splitter 158 and is separately input to both downstreamreceiver 150 and upstream transmitter 160 as a “pure” unmodulated signalfor Ch1′. In this alternative embodiment, second unmodulated signal 170(Ch1′) thus functions a seed signal for upstream transmitter 160 and a“pseudo LO signal” for downstream receiver 150 for the coherentdetection of Ch1. For purposes of this discussion, second unmodulatedsignal 170 (Ch1′) is referred to as a “pseudo LO signal” because it usesan LO signal from a remote source (output from first hub opticaldemultiplexer 124), and is not required to produce an LO signal locallyat end device 106. This particular configuration further significantlyreduces cost and complexity of the architecture of the system 100 by thereduction of necessary electronic components.

For upstream transmission, in an embodiment, a similar coherentdetection scheme is implemented for upstream transmitter 160 as isutilized for downstream transmitter 126. That is, second unmodulatedsignal 170 (Ch1′) is input to upstream optical circulator 162 andmodulated by upstream modulator 164 to adhere symmetric or asymmetricdata (not shown, described below with respect to FIG. 6) utilizing oneor more slave lasers (also not shown, described below with respect toFIG. 6), and then output as an upstream modulated data stream 176(Ch1′), which is then combined with similar modulated data streams fromother channels (not shown) by a node multiplexer 178 in fiber node 104.Second unmodulated signal 170 (Ch1′) is then transmitted upstream overupstream fiber 110, separated from other channel signals by second huboptical demultiplexer 134, an input to upstream receiver 132, forsimplified digital signal processing similar to the process describedabove with respect to downstream receiver 150.

By this configuration, multiple upstream channels from different enddevices 106 can be multiplexed at fiber node 104 (or a remote node) andsent back to optical hub 102. Thus, within optical hub 102, the samecoherent detection scheme may be used at upstream receiver 132 as isused with downstream receiver 150, except that upstream receiver 132utilizes first unmodulated signal 168 (Ch1) as the LO and upstreammodulated data stream 176 (Ch1′) to carry data, whereas downstreamreceiver 150 utilizes the data stream pair (Ch1, Ch1′) in reverse. Thatis, downstream receiver 150 utilizes second unmodulated signal 170(Ch1′) as the LO and downstream modulated data stream 172 (Ch1) to carrydata.

Implementation of the embodiments described herein are useful formigrating hybrid fiber-coaxial (HFC) architectures towards other typesof fiber architectures, as well as deeper fiber architectures. TypicalHFC architectures tend to have very few fiber strands available fromfiber node to hub (e.g. fibers 108, 110), but many fiber strands couldbe deployed to cover the shorter distances that are typical from legacyHFC nodes to end devices (e.g., fiber optics 112). In the embodimentsdescribed herein, two fibers (i.e., fibers 108, 110) are illustratedbetween optical hub 102 and fiber node 104, which can be a legacy HFCfiber node. That is, one fiber (i.e., downstream fiber 108) is utilizedfor downstream signal and upstream seed/downstream LO, and another fiber(i.e., upstream fiber 110) is utilized for upstream signal.Additionally, three fibers (i.e., fiber optics 112A-C) are illustratedfor each end device from fiber node 104 (e.g., legacy HFC fiber node) toend device 106. By utilization of the advantageous configurationsherein, fiber deeper or all-fiber migration schemes can utilize an HFCfiber node as an optical fiber distribution node, thereby greatlyminimizing the need for fiber retrenching from an HFC node to an opticalhub.

The architecture described herein, by avoiding the need for conventionalcompensation hardware, can therefore be structured as a significantlyless expensive and more compact physical device than conventionaldevices. This novel and advantageous system and subsystem arrangementallows for multi-wavelength emission with simplicity, reliability, andlow cost. Implementation of optical frequency comb generator 114, withhigh quality input source signal 116, further allows simultaneouscontrol of multiple sources that are not realized by conventionaldiscrete lasers. According to the embodiments herein, channel spacing,for example, may be 25 GHz, 12.5 GHz, or 6.25 GHz, based on availablesignal bandwidth occupancy.

The embodiments described herein realize still further advantages byutilizing a comb generator (i.e., optical frequency comb generator 114)that maintains a constant wavelength spacing, thereby avoiding opticalbeat interference (OBI) that may be prevalent in cases with simultaneoustransmissions over a single fiber. In the embodiment illustrated in FIG.1, fiber node 104 is shown as a passive system, and is thus expected tomaintain a higher reliability than other migration approaches.Nevertheless, one of ordinary skill in the art, after reading andcomprehending present application, will understand how the embodimentsdisclosed herein may also be adapted to a remote physical solution, orto a remote cable modem termination system (CMTS) that is included inthe fiber node.

As illustrated and described herein, system 100 may utilize anarchitecture of coherent DWDM-PON incorporate novel solutions to meetthe unique requirements of access environment, but with cost-efficientstructures not seen in conventional hardware systems. Optical frequencycomb generator 114 produces a plurality of simultaneous narrow widthwavelength channels with controlled spacing, thereby allowing simplifiedtuning of the entire wavelength comb. This centralized comb light sourcein optical hub 102 therefore provides master seeding sources and LOsignals for both downstream and upstream directions in heterodynedetection configurations in order to reuse the optical sourcesthroughout the entirety of system 100. This advantageous configurationrealizes significant cost savings and reduction in hardware complexityover intradyne detection schemes in long-haul systems, for example.

FIG. 2 is a schematic illustration depicting a downstream transmitter200 that can be utilized with fiber communication system 100, depictedin FIG. 1. Downstream transmitter 200 includes downstream opticalcirculator 136 (see FIG. 1, above) in two-way communication with a laserinjected modulator 202, which includes a laser diode 204, which receivesdata 206 from an external data source 208. In an alternative embodiment,downstream transmitter 200 may include two separate fiber receivers (notshown), which would substitute, and eliminate the need, for downstreamoptical circulator 136 in the structural configuration shown.

In operation, downstream transmitter 200 performs the same generalfunctions as downstream transmitter 126 (FIG. 1, described above). Laserinjected modulator 202 utilizes laser diode 204 as a “slave laser.” Thatis, laser diode 204 is injection locked by external laser 118, whichfunctions as a single frequency or longitudinal mode master, or seed,laser to keep the frequency of a resonator mode of laser diode 204 closeenough to the frequency of the master laser (i.e., laser 118) to allowfor frequency locking. The principle of downstream transmitter 200 isalso referred to as “laser cloning,” where a single high quality masterlaser (i.e., laser 118) transmits a narrow bandwidth, low noise signal(i.e., source signal 116), and a relatively inexpensive slave laser(e.g., laser diode 204) can be used throughout system 100 to transmitdata modulated signals, such as downstream modulated data stream 172(Ch1). In an embodiment, laser diode 204 is a Fabry Perot laser diode(FP LD), or a vertical-cavity surface-emitting laser (VCSEL), incomparison with the considerably more expensive distributed feedbacklaser diodes (DFB LD) that are conventionally used. In an alternativeembodiment, laser diode 204 is an LED, which can perform as a sufficientslave laser source according to the embodiments herein due to theutilization of the high quality source signal 116 that is consistentlyutilized throughout system 100.

More specifically, first unmodulated signal 168 (Ch1) exiting huboptical splitter 130 is input to downstream optical circulator 136,which then excites laser diode 204, that is, laser diode 204 emits lightat a specified modulation rate. Laser injected modulator 202 adheresdata 206 to the excited Ch1 signal, and the resultant modulated Ch1signal with adhered data is output from downstream optical circulator136 as downstream modulated data stream 172 (Ch1). According to thisembodiment, first unmodulated signal 168 (Ch1) is input to downstreamtransmitter 126 as an unmodulated, low amplitude, narrow bandwidth, lownoise “pure” source, and is modulated by laser diode 204, which is ahigh amplitude, wide bandwidth device, and resultant downstreammodulated data stream 172 (Ch1) is a high amplitude, narrow bandwidth,low noise “pure” signal that can be transmitted throughout system 100without the need for further conventional compensation means (hardwareand programming). Suppression of adjacent longitudinal modes from laserdiode 204, for example, is not necessary because of the exciting sourcesignal (i.e., signal 168) is of such high quality and narrow bandwidththat output downstream modulated data stream 172 (Ch1) is substantiallyamplified only within the narrow bandwidth of external laser 118. In theembodiment illustrated in FIG. 2, laser injected modulator 202implements direct modulation.

Optical injection locking as described herein thus improves upon theperformance of the relatively less expensive, multi-longitudinal slavelaser source (i.e., laser diode 204) in terms of spectral bandwidth andnoise properties. With respect to heterodyne coherent detection,incoming signals (upstream or downstream) can be combined with the LO orpseudo-LO and brought to an intermediate frequency (IF) for electronicprocessing. According to this configuration, part of the LO/pseudo-LOoptical power can also be employed as the master/seed laser for thereverse transmission direction, at both optical hub 102, and at enddevice 106 (described below with respect to FIG. 6), and thus a fullycoherent system having a master seed and LO delivery from an optical hubcan be achieved in a relatively cost-effective manner comparison withconventional systems.

FIG. 3 is a schematic illustration depicting an alternative downstreamtransmitter 300 that can be utilized with fiber communication system100, depicted in FIG. 1. Downstream transmitter 300 is similar todownstream transmitter 200 (FIG. 2), including the implementation ofdirect modulation, except that downstream transmitter 300 alternativelyutilizes polarization division multiplexing to modulate the Ch1 signalinto downstream modulated data stream 172 (Ch1).

Downstream transmitter 300 includes downstream optical circulator 136(see FIG. 1, above) in two-way communication with a laser injectedmodulator 302, which includes a polarization beam splitter(PBS)/polarization beam combiner (PBC) 304, which can be a singledevice. Laser injected modulator 302 further includes a first laserdiode 306 configured to receive first data 308 from an external datasource (not shown in FIG. 3), and a second laser diode 310 configured toreceive second data 312 from the same, or different, external datasource.

In operation, downstream transmitter 300 is similar to downstreamtransmitter 200 with respect to the implementation of direct modulation,and master/slave laser injection locking. Downstream transmitter 300though, alternatively implements dual-polarization from the splitterportion of PBS/PBC 304, which splits first unmodulated signal 168 (Ch1)into its x-polarization component P1 and y-polarization component P2,which separately excite first laser diode 306 and second laser diode310, respectively. Similar to downstream transmitter 200 (FIG. 2), indownstream transmitter 300, first unmodulated signal 168 (Ch1) exitinghub optical splitter 130 is input to downstream optical circulator 136,the separate polarization components of which then excite laser diodes306, 310, respectively, at the specified modulation rate. Laser injectedmodulator 302 adheres data first and second data 308, 312 to therespective excited polarization components of the Ch1 signal, which arecombined by the combiner portion of PBS/PBC 304. The resultant modulatedCh1 signal with adhered data is output from downstream opticalcirculator 136 as downstream modulated data stream 172 (Ch1).

In an embodiment, the polarized light components received by first andsecond laser diodes 306, 310 are orthogonal (90 degrees and/ornoninteractive). That is, first laser diode 306 and second laser diode310 are optimized as slave lasers to lock onto the same wavelength asexternal laser 118 (master), but with perpendicular polarizationdirections. By this configuration, large data packets (e.g., first data308 and second data 312) can be split and simultaneously sent alongseparate pathways before recombination as downstream modulated datastream 172 (Ch1). Alternatively, first data 308 and second data 312 maycome from two (or more) separate unrelated sources. The orthogonal splitprevents data interference between the polarized signal components.However, one of ordinary skill in the art will appreciate that,according to the embodiment of FIG. 3, first unmodulated signal 168(Ch1) can also be polarized at 60 degrees, utilizing similar principlesof amplitude and phase, as well as wavelength division. Firstunmodulated signal 168 (Ch1) can alternatively be multiplexed accordingto a spiral or vortex polarization, or orbital angular momentum.Additionally, whereas the illustrated embodiment features polarizationmultiplexing, space division multiplexing and mode division multiplexingmay be also alternatively implemented.

According to this embodiment, master continuous wave signal for Ch1,namely, first unmodulated signal 168, is received from optical frequencycomb generator 114 and is split to be used, in the first part, as the LOfor upstream receiver 132, and in the second part, to synchronize twoslave lasers (i.e., first laser diode 306 and second laser diode 310) bythe respective x-polarization and y-polarization light portions suchthat both slave lasers oscillate according to the wavelength of themaster laser (i.e., external laser 118). Data (i.e., first data 308 andsecond data 312) is directly modulated onto the two slave lasers,respectively. This injection locking technique thus further allows forfrequency modulation (FM) noise spectrum control from the master laserto the slave laser, and is further able to realize significantimprovements in FM noise/phase jitter suppression and emission linewidthreduction.

As described herein, utilization of optical injection with adual-polarization optical transmitter (e.g., downstream transmitter 300)by direct modulation may advantageously implement relatively lower-costlasers to perform the functions of conventional lasers that areconsiderably more expensive. According to this configuration of adual-polarization optical transmitter by direct modulation ofsemiconductor laser together with coherent detection, the presentembodiments are particular useful for short-reach applications in termsof its lower cost and architectural compactness. Similar advantages maybe realized for long reach applications.

FIG. 4 is a schematic illustration depicting an alternative downstreamtransmitter 400 that can be utilized with fiber communication system100, depicted in FIG. 1. Downstream transmitter 400 is similar todownstream transmitter 200 (FIG. 2), except that downstream transmitter400 alternatively implements external modulation, as opposed to directmodulation, to modulate the Ch1 signal into downstream modulated datastream 172 (Ch1). Downstream transmitter 400 includes downstream opticalcirculator 136 (see FIG. 1, above) and a laser injected modulator 402.Downstream optical circulator 136 is in one-way direct communicationwith a separate external optical circulator 404 that may be containedwithin laser injected modulator 402 or separate. Laser injectedmodulator 402 further includes a laser diode 406, which receives the lowamplitude, narrow bandwidth, first unmodulated signal 168 (Ch1) andemits an excited, high amplitude, narrow bandwidth, optical signal 408back to external optical circulator 404. Laser injected modulator 402still further includes an external modulating element 410, whichreceives data 412 from an external data source 414, and adheres data 412with optical signal 408 to be unidirectionally received back bydownstream optical circulator 136 and output as downstream modulateddata stream 172 (Ch1).

In this embodiment, downstream transmitter 400 performs the same generalfunctions as downstream transmitter 126 (FIG. 1, described above), butuses external modulation as the injection locking mechanism to locklaser diode 406 to the wavelength of the master laser source (e.g.,external laser 118). To implement external modulation, this embodimentregulates optical signal flow through mostly unidirectional opticalcirculators (i.e., downstream optical circulator 136, external opticalcirculator 404). External modulating element 410 may optionally includea demultiplexing filter (not shown) as an integral component, orseparately along the signal path of downstream modulated data stream 172(Ch1) prior to input by downstream receiver 150. In an embodiment,external modulating element 410 is a monitor photodiode, and injectionlocking is performed through a rear laser facet.

FIG. 5 is a schematic illustration depicting an alternative downstream500 transmitter that can be utilized with fiber communication system100, depicted in FIG. 1. Downstream transmitter 500 is similar todownstream transmitter 300 (FIG. 3), including the implementation ofdirect modulation and polarization division multiplexing, except thatdownstream transmitter 500 further implements quadrature amplitudemodulation (QAM) to modulate the Ch1 signal into downstream modulateddata stream 172 (Ch1). That is, further external modulating elements maybe utilized per polarization branch (FIG. 2, above) to generate QAMsignals.

Downstream transmitter 500 includes downstream optical circulator 136(see FIG. 1, above) in two-way communication with a laser injectedmodulator 502, which includes a PBS/PBC 504, which can be a singledevice or two separate devices. Additionally, all of the components oflaser injected modulator 502 may themselves be separate devices, oralternatively all contained within a single photonic chip. Laserinjected modulator 502 further includes a first laser diode 506configured to receive first data 508 from an external data source (notshown in FIG. 5), a second laser diode 510 configured to receive seconddata 512 from the same, or different, external data source, a thirdlaser diode 514 configured to receive third data 516 from thesame/different, external data source, and a fourth laser diode 518configured to receive fourth data 520 from the same/different externaldata source.

In operation, downstream transmitter 500 implements dual-polarizationfrom the splitter portion of PBS/PBC 504, which splits first unmodulatedsignal 168 (Ch1) into its x-polarization component (P1) andy-polarization component (P2). Each polarization component P1, P2 isthen input to first non-polarized optical splitter/combiner 522 andsecond non-polarized optical splitter/combiner 524, respectively. Firstand second optical splitters/combiners 522, 524 each then further splittheir respective polarization components P1, P2 into their I-signals526, 528, respectively, and also into their Q-signals 530, 532,respectively. Generated I-signals 526, 528 then directly excite laserdiodes 506, 514, respectively. Before directly communicating with laserdiodes 510, 518, respectively, generated Q-signals 530, 532 first passthrough first and second quadrature phase shift elements 534, 536,respectively, each of which shifts the Q-signal by 45 degrees in eachdirection, such that the respective Q-signal is offset by 90 degreesfrom its respective I-signal when recombined at splitters/combiners 522,524.

The resultant modulated Ch1 signal, with adhered data, is output fromdownstream optical circulator 136 of downstream transmitter 500 asdownstream modulated data stream 172 (Ch1), and as a polarized,multiplexed QAM signal. According to this embodiment, utilization of aphotonic integrated circuit allows for directly modulated polarizationof a multiplexed coherent system, but utilizing significantly lower costhardware configurations than are realized by conventional architectures.In an embodiment, laser diodes 506, 510, 514, 516 are PAM-4 modulatedlaser diodes capable of generating 16-QAM polarization multiplexedsignals.

FIG. 6 is a schematic illustration depicting an upstream transmitter 600that can be utilized with the fiber communication system 100, depictedin FIG. 1. In the embodiment illustrated in FIG. 6, upstream transmitter600 is similar to downstream transmitter 300 (FIG. 3) in structure andfunction. Specifically, upstream transmitter 600 includes upstreamoptical circulator 162 (see FIG. 1, above) in two-way communication witha laser injected modulator 602 (not separately illustrated in FIG. 6),which includes a PBS/PBC 604, which can be a single device or separatedevices. Laser injected modulator 602 further includes a first laserdiode 606 configured to receive first data 608 from an external datasource (not shown in FIG. 6), and a second laser diode 610 configured toreceive second data 612 from the same, or different, external datasource. Similar to the embodiments of FIGS. 2-5, above, downstreamtransmitter 600 may also eliminate for upstream optical circulator 162by the utilization of at least two separate fiber receivers (not shown).

Upstream transmitter 600 is thus nearly identical to downstreamtransmitter 300 (FIG. 3), except that upstream transmitter 600 utilizessecond unmodulated signal 170 (Ch1′) as the end device seed source, inlaser injected modulator 602, to combine or adhere with data (e.g.,first data 608, second data 612) to generate upstream modulated datastream 176 (Ch1′) to carry upstream data signals to an upstream receiver(e.g., upstream receiver 132). In operation, first laser diode 606 andsecond laser diode 610 also function as slave lasers by injectionlocking to the master signal from external laser 118. That is, symmetricor asymmetric data for Ch1′ (e.g., first data 608, second data 612) ismodulated onto the two slave lasers (i.e., first laser diode 606 andsecond laser diode 610) with polarization multiplexing, much the same asthe process implemented with respect to downstream transmitter 300 (FIG.3) in optical hub 102.

In this example, upstream transmitter 600 is illustrated tosubstantially mimic the architecture of downstream transmitter 300 (FIG.3). Alternatively, upstream transmitter 600 could equivalently mimic thearchitecture of one or more of downstream transmitters 200 (FIG. 2), 400(FIG. 4), or 500 (FIG. 5) without departing from the scope of thepresent disclosure. Furthermore, upstream transmitter 600 can conform toany of the embodiments disclosed by FIGS. 2-5, irrespective of thespecific architecture of the particular downstream transmitter utilizedwithin optical hub 102. By utilization of high-quality, narrowbandwidth, low noise external laser source 118, the master/slave laserrelationship carries through the entirety of system 100, and theplurality of end devices 106 that receive modulated/unmodulated signalpairs (which may be 32, 64, 128, or as many as 256 from a single fiberline pair, e.g., downstream fiber 108 and upstream fiber 110).

The significant cost savings according to the present embodiments arethus best realized when considering that as many as 512 downstreamtransmitters (e.g., downstream transmitter 126, FIG. 1) and upstreamtransmitters (e.g., upstream transmitter 160, FIG. 1) may be necessaryto fully implement all available chattel pairs from a single optical hub102. The present embodiments implement a significantly lower cost andless complex hardware architecture to utilize the benefits accruing fromimplementation of high-quality external laser 118, without having to addexpensive single longitudinal mode laser diodes, or other compensationhardware necessary to suppress adjacent longitudinal modes frominexpensive lasers or the noise components produced thereby.

FIG. 7 is a schematic illustration depicting a processing architecturewhich can be implemented for upstream receiver 132, downstream receiver150, and fiber communication system 100, depicted in FIG. 1. Therespective architectures of upstream receiver 132 and downstreamreceiver 150 are similar with respect to form and function (describedabove with respect to FIG. 1), except that upstream receiver 132receives a first data stream pair 700 for Ch1, Ch1′, in reverse of asecond data stream pair 702, which is received by downstream receiver150. In other words, as described above, first data stream pair 700includes first unmodulated signal 168 (Ch1) as the LO and upstreammodulated data stream 176 (Ch1′) to carry data, whereas second datastream pair 702 includes unmodulated signal 170 (Ch1′) as the LO anddownstream modulated data stream 172 (Ch1) to carry data.

First and second data stream pairs 700, 702 the multiplexed phasesynchronized pairs modulated/unmodulated of optical signals that areconverted into analog electrical signals by ICR 140 and ICR 152,respectively. The respective analog signals are then converted intodigital domain by ADC 142 and ADC 154, for digital signal processing byDSP 144 and DSP 156. In an embodiment, digital signal processing may beperformed by a CMOS ASIC employing very large quantities of gate arrays.A conventional CMOS ASIC, for example, can utilize as many as 70 milliongates to process incoming digitized data streams. In the conventionalsystems, modulated data streams for Ch1 and Ch1′ are processedindependently, which requires significant resources to estimatefrequency offset, drift, and digital down conversion compensationfactors (e.g., e{circumflex over ( )}-jωt, where ω represents thefrequency difference between first unmodulated signal 168 and upstreammodulated data stream 176, and ω is held constant for coherent tone pair166, as extended throughout system 100).

According to the embodiments disclosed herein, on the other hand, themodulated and unmodulated signals from Ch1 and Ch1′ are phasesynchronized together such that the difference between ω of the signalpair is always known, and phase synchronized to maintain a constantrelationship. In contrast, conventional systems are required toconstantly estimate the carrier phase to compensate for factors such asdraft which requires considerable processing resources, as discussedabove. According to the present embodiments though, since Ch1 and Ch1′are synchronized together as first and second data stream pairs 700,702, the offset ω between the pairs 700, 702 need not be estimated,since it may be instead easily derived by a simplified subtractionprocess in DSP 144 and DSP 156 because the signal pairs will drifttogether by the same amount in a constant relationship. By thisadvantageous configuration and process, digital signal processing by aCMOS ASIC can be performed utilizing as few as one million gates,thereby greatly improving the processing speed of the respective DSP,and/or reducing the number of physical chips required to perform theprocessing (or similarly increasing the amount of separate processingthat may be performed by the same chip). At present, implementation ofthe embodiments described herein may improve downstream and upstreamdata transmission speeds by as much as 5000 times faster thanconventional systems.

FIG. 8 is a flow chart diagram of a downstream optical network process800 that can be implemented with fiber communication system 100,depicted in FIG. 1. Process 800 begins at step 802. In step 802,coherent tone pairs 166 are generated and output by optical frequencycomb generator 114, amplifier 122, and first hub optical demultiplexer124. Similar to the discussion above, for simplification purposes, thefollowing discussion addresses specific coherent tone pair 166(1) forCh1, Ch1′. Coherent tone pair 166 includes first unmodulated signal 168(Ch1) and second unmodulated signal 170 (Ch1′). Once coherent tone pair166 is generated, process 800 proceeds from step 802 to steps 804 and806, which may be performed together or simultaneously.

In step 804, first unmodulated signal 168 (Ch1) is input to an opticalsplitter, e.g., optical splitter 130, FIG. 1. In step 806, secondunmodulated signal 170 (Ch1′) is transmitted to a multiplexer, e.g., huboptical multiplexer 128, FIG. 1. Referring back to step 804, firstunmodulated signal 168 (Ch1) is split to function both as an LO forupstream detection, and as a seed for downstream data transmission. Forupstream detection, step 804 proceeds to step 808, where firstunmodulated signal 168 (Ch1) is received by an upstream receiver, i.e.,upstream receiver 132, FIG. 1. For downstream data transmission, step804 separately and simultaneously proceeds to step 810.

Step 810 is an optional step, where polarization division multiplexingis desired. In step 810, first unmodulated signal 168 (Ch1) is splitinto its x-component and y-component parts P1, P2, respectively (e.g.,by PBS/PBC 304, FIG. 3 or PBS/PBC 504, FIG. 5) for separate direct orexternal modulation. Where polarization division multiplexing is notutilized, process 800 skips step 810, and instead proceeds directly fromstep 804 to step 812. In step 812, first unmodulated signal 168 (Ch1),or its polarized components if optional step 810 is implemented, ismodulated by direct (e.g., FIGS. 2, 3, 5) or external (e.g., FIG. 4)modulation. Process 800 then proceeds from step 812 to step 814. Step814 is an optional step, which is implemented if optional step 810 isalso implemented for polarization division multiplexing. In step 814,the x-component and y-component parts P1, P2 are recombined (e.g., byPBS/PBC 304, FIG. 3 or PBS/PBC 504, FIG. 5) for output as downstreammodulated data stream 172 (Ch1). Where polarization divisionmultiplexing was not utilized, process 800 skips step 814, and insteadproceeds directly from step 812 to step 816.

In step 816, second unmodulated signal 170 (Ch1′) and downstreammodulated data stream 172 (Ch1) are optically multiplexed, i.e., by huboptical multiplexer 128, FIG. 1, as a phase synchronized data streampair (e.g., second data stream pair 702, FIG. 7). Process 800 thenproceeds from step 816 to step 818, where the phase synchronized datastream pair is transmitted over an optical fiber, i.e., downstream fiber108, FIG. 1. Process 800 then proceeds from step 818 to step 820, wherethe synchronized data stream pair is optically demultiplexed, e.g., bynode optical demultiplexer 174 in fiber node 104. Process 800 thenproceeds from step 820 to step 822, where both components of thedemultiplexed data stream pair (e.g., second unmodulated signal 170(Ch1′) and downstream modulated data stream 172 (Ch1)) are received by adownstream receiver (e.g., downstream receiver 150, FIG. 1) forheterodyne coherent detection.

Where an end device (e.g., end device 106) further includes upstreamtransmission capability, process 800 further includes optional steps 824and 826. In step 824, and prior to downstream reception in step 822,second unmodulated signal 170 (Ch1′) is optically split (e.g., by enddevice optical splitter 158, FIG. 1), and additionally transmitted, instep 826, to an upstream transmitter of the end device (e.g., upstreamtransmitter 160, FIG. 1) as a seed signal for a modulator (e.g.,modulator 164, FIG. 1) for upstream data transmission, as explainedfurther below with respect to FIG. 9.

FIG. 9 is a flow chart diagram of an upstream optical network process900 that can be optionally implemented with fiber communication system100, depicted in FIG. 1. Process 900 begins at optional step 902. Instep 902, where polarization division multiplexing is utilized in theupstream transmitter (e.g., upstream transmitter 160, FIG. 1), secondunmodulated signal 170 (Ch1′) (from step 826, FIG. 8) is split into itsx-component and y-component parts (e.g., by PBS/PBC 604, FIG. 6) forseparate direct or external modulation. Where polarization divisionmultiplexing is not utilized, step 902 is skipped, and process 900instead begins at step 904.

In step 904, second unmodulated signal 170 (Ch1′), or its polarizedcomponents if optional step 902 is implemented, is injection locked tothe master source laser (e.g., external laser 118, FIG. 1), as describedabove with respect to FIGS. 1 and 6. Step 904 then proceeds to step 906,where injection locked signal is modulated by direct or externalmodulation. Process 900 then proceeds from step 906 to step 908. Step908 is an optional step, which is implemented if optional step 902 isalso implemented for polarization division multiplexing. In step 908,the x-component and y-component parts of the excited Ch1′ signal arerecombined (e.g., by PBS/PBC 604, FIG. 6) for output as upstreammodulated data stream 176 (Ch1′). Where polarization divisionmultiplexing was not utilized, process 900 skips step 908, and insteadproceeds directly from step 906 to step 910.

In step 910, upstream modulated data stream 176 (Ch1′) is opticallymultiplexed, i.e., by node optical multiplexer 178, FIG. 1, with otherupstream data stream signals (not shown). Process 900 then proceeds fromstep 910 to step 912, where upstream modulated data stream 176 (Ch1′) istransmitted over an optical fiber, i.e., upstream fiber 110, FIG. 1.Process 900 then proceeds from step 912 to step 914, where upstreammodulated data stream 176 (Ch1′) is optically demultiplexed, e.g., bysecond hub optical demultiplexer 134, which separates the selected datastream from the other upstream data stream signals, for transmission toa particular upstream receiver tuned to receive the modulated datastream. Process 900 then proceeds from step 914 to step 916, where bothcomponents (e.g., first unmodulated signal 168 (Ch1), FIG. 8, andupstream modulated data stream 176 (Ch1′)) of the upstream data streampair, e.g., first data stream pair 700, FIG. 7, are received by anupstream receiver (e.g., upstream receiver and 32, FIG. 1) forheterodyne coherent detection.

FIG. 10 is a schematic illustration of a fiber communication system 1000that supports network communication systems and methods in accordancewith an embodiment of the present disclosure. System 1000 may includehub 1005, fiber nodes 1010, end devices 1025, and a base station 1030.Hub 1005 may be an optical hub 1005 that is, for example, a centraloffice, a communications hub, or an optical line terminal (OLT). In theembodiment shown, fiber node 1010 is illustrated for use with an opticalnetwork, such as but not limited to a passive optical network (PON) andits variants. End devices 1025 may be downstream termination units,which can represent, for example, a customer device, customer premises(e.g., an apartment building), a business user, or an optical networkunit (ONU). Base station 1030 is shown as a larger wireless station,such as a macro cell, but may equally, optionally or additionallyinclude one or more small cells, micro cells, picocells, femtocell, andother versions of radio heads and remote radio heads including split andvirtualized and particularly virtualized radio units. In an embodiment,system 1000 utilizes a coherent Dense Wavelength Division Multiplexing(DWDM) PON architecture. The fiber communication system 1000 may useaspects of fiber communication system 100 as described with reference toFIGS. 1 through 7. For example, the fiber node 1010 may include aspectsof optical hub 102 and/or fiber node 104. In another example, enddevices 1025 may include aspects of end devices 106.

Hub 1005 may communicate with fiber node 1010-a by way of optical fiberbundle 1015. Optical fiber bundle 1015 may be used to communicate bothdownstream communications to fiber node 1010-a and upstreamcommunications from fiber node 1010-a to hub 1005. In operation, opticalfiber bundle 1015 may be typically 30 km or shorter. However, accordingto the embodiments presented herein, greater lengths are contemplated,such as between 100 km and 1000 km. In some cases, optical fiber bundle1015 may include only a single fiber or a few individual fibers (e.g.,six). In an embodiment, fiber node 1010-a may connect with other devicesby optical fibers 1020. For example, fiber node 1010-a may connect withend device 1025-a by optical fiber 1020-a and fiber nodes 1010-b and1010-c by optical fibers 1020-d and 1020-b respectively. In some cases,fiber node 1010-a and end device 1025-a may be integrated as a singledevice, such as a modem, which may be located at or near a customerpremises. In cases when the fiber node 1010-a and other devices (e.g.,end device 1025-a, fiber nodes 1010-b, 1010-c, base station 1030) areseparate devices, optical fibers 1020 may span distances ofapproximately 5000 feet or less, although this is not required. Thesystem 1000 may correspond to an optical service domain group. Theoptical service domain group may correspond to a group of devicesrouting communications through fiber node 1010-a.

Fiber node 1010-a may be configured to multiplex and aggregate servicesover fiber access networks, such as but not limited to a cable accessnetwork and other access networks. For example, fiber node 1010-a mayreceive downstream communications and direct the downstreamcommunications by optical fibers 1020 to one or more of the devices(e.g., end devices 1025, fiber nodes 1010, base station 1030). Thedownstream communications may carry DOCSIS channels, digital video,analog video channels, channels with telemetry information, set top boxcontrol channels, IP protocol data, over-the-top data, telephonychannels, and any other data that may be carried over digital and analognetworks. In another example, system 1000 may include EPON services,RFOG services, in combination with other services.

Fiber node 1010-a may receive and aggregate upstream communications fromend device 1025-a, fiber nodes 1010-b, or base station 1030. Theupstream communications may include DOCSIS channels, set top box returnchannels, upstream telemetry, and telephony channels. The upstreamcommunications may also include EPON, Gigabit PON, RFOG, and GigabitEthernet. In some cases, the channels may be multiplexed and a widebandcomposite signal may be used to intensity modulate an optical carrier(e.g., by an end device 1025). The fiber node 1010-a may combine theupstream signals and communicate them to hub 1005. Fiber node 1010-a maydirect communications to other fiber nodes 1010. For example, the fibernode 1010-a may receive downstream communications from hub 1005 anddirect the communications to other fiber nodes 1010 (e.g., fiber nodes1010-b and 1010-c). Here, the receiving fiber nodes 1010-b and 1010-cmay in turn receive the downstream communications from fiber node 1010-aand direct the communications accordingly. For example, fiber node1010-b may receive downstream communications from fiber node 1010-a anddirect the communications to end devices 1025-b and 1025-c by fibers1020-e and 1020-f. Further, fiber node 1010-b may receive and aggregateupstream communications from end devices 1025-b and 1025-c and fibernode 1010-b may direct the upstream communications to fiber node 1010-a.In some examples, end devices 1025 may be homes, businesses, and soforth.

The system 1000 may be or include a hybrid fiber-coaxial (HFC) network.An HFC network may include both optical fibers 1020 and coaxial cables.In a case when system 1000 includes coaxial cables, fiber nodes 1010 mayreceive and direct communications by optical fibers and coaxial cables.For example, fiber node 1010-c may receive downstream communicationsfrom fiber node 1010-a by optical fiber 1020-b and direct the downstreamcommunications by coaxial cables to end devices 1025-d and 1025-e.System 1000 may include one or more RF amplifiers 1035. The RFamplifiers 1035 may be used to amplify signals being communicated by acoaxial cable. For example, RF amplifier 1035 may be used to amplify asignal between fiber node 1010-c and end device 1025-e. In some cases, anumber or placement of RF amplifiers 1035 may be based on a number offactors such as a length of coaxial cable, a type of signal beingcommunicated on the coaxial cable, or an amount of noise associated withthe signals being communicated on the coaxial cable.

Fiber node 1010-a may be configured to direct communications formultiple industries. That is, fiber node 1010-a may direct opticalcommunications as well as wireless communications. For example, system1000 may be used for point-to-point optical link based services, such asGigabit Ethernet (e.g., used to support business services). In anotherexample, fiber node 1010-a may connect base station 1030 to a backhaulnetwork (e.g., establish a wired communication between the base station1030 and the hub 1005) by optical fiber 1020-c. Alternatively, fibernode 1010-a may connect base station 1030 to a fronthaul, mid-haul orx-haul network, depending on the network configuration and/or coupling.Base station 1030 has been included for explanatory purposes only andsystem 1000 may include one or more base stations 1030 or no basestations. In some cases, the system 100 may include one or more accesspoints or other types of radio units.

The system 1000 may enable multiple transmissions (e.g., downstreamtransmissions to one or more end devices 1025, upstream transmissionsfrom one or more end devices) at the same time. For example, system 1000may be, but not limited to, an RFOG system. Certain types of RFOGsystems may enable simultaneous upstream transmissions. Here, multiplesimultaneous transmissions may be allowed in synchronous code divisionmultiple access (S-CDMA) mode and also in DOCSIS 3.0 mode. That is,there may be a first transmission (e.g., by a first device such as anend device 1025, fiber node 1010, or base station 1030) on a firstchannel at the same time that another device transmits on otherchannels. Additionally or alternatively, system 1000 may enabletransmissions corresponding to different services or optical networks(e.g., PON, RFOG, EPON, Gigabit PON, SPON, AON, etc.).

Simultaneous transmissions and transmissions from different services mayresult in OBI. For example, if two devices transmit using wavelengthsclose enough in frequency such that their difference falls within thefrequency response of the optical receiver, their transmissions maycause OBI. Different techniques may be used to eliminate, minimizeand/or control OBI.

System 1000 may ensure that upstream transmissions are maintainedaccording to certain wavelength windows. For example, fiber node 1010-amay provide more than one seed source (e.g., narrow wavelength bands)and transmit the seed sources to end devices 1025, fiber nodes 1010, andbase station 1030. The seed sources may be maintained within constraintsof wavelength filter windows (e.g., fiber node 1010-a may providewavelength bands in order to avoid or minimize OBI). The fiber node1010-a may transmit a seed source with a unique wavelength band to eachof the devices (e.g., end devices 1025, fiber nodes 1010, and basestation 1030). The devices may provide upstream communications accordingto the received wavelength band, thus minimizing OBI resulting insimultaneous upstream communications from the devices or communicationsby different services.

By placing the seed sources at the fiber node (e.g., closer to the enddevices 1025 when compared to placing the seed sources at the hub 1005),the seed signals may be stronger for injection locking at the enddevices 1025. This may reduce a complexity of the seed sources.

FIG. 11 is a schematic illustration of a communication system 1100 thatsupports network communication systems and methods in accordance with anembodiment of the present disclosure. The system 1100 may include one ormore components as described with reference to FIGS. 1-7 and 10. Forexample, the system 1100 may include a hub 1105 in communication with afiber node 1110. The hub 1105 and fiber node 1110 may be example of hub1005 and fiber nodes 1010 as described with reference to FIG. 10.Further, the system 1100 may include end devices 1125 which may beexamples of end devices 1025 as described with reference to FIG. 10. Theend devices 1125 may be downstream termination units, base stations(e.g., such as base station 1030 as described with reference to FIG.10), or other fiber nodes 1110. System 1100 may be a passive opticalnetwork (PON) and, in some cases, may reduce (e.g., eliminate) OBI.

In operation, fiber node 1110 may perform the same general functions asfiber node 1010-a as described with reference to FIG. 10. Fiber node1110 may direct downstream communications from hub 1105 to end devices1125 and upstream communications from end devices 1125 to the hub 1105.System 1100 may detail the components and data flow for upstreamcommunications. Fiber node 1110 may aggregate the upstreamcommunications by optical splitter 1170, which may output an aggregatedupstream communication (e.g., a single upstream communication includingthe upstream communications from end device 1125-a, 1125-b, and 1125-c).The number of ports of the optical splitter 1170 may define the size ofthe optical service domain group. The optical splitter 1170 may achievelow loss (e.g., when compared to a fused fiber coupler). In some cases,the combining loss (e.g., a loss of power when aggregating multipleupstream transmissions) using the optical splitter 1170 may be lower(e.g., when compared to a combining loss using a fused fiber coupler)when the number of upstream transmissions is high. Alternatively, awavelength multiplexer may be used instead of the optical splitter 1170which may result in lower losses when a number of ports is high. Fibernode 1110 may facilitate the transmission of the aggregated upstreamcommunication via optical fiber 1115 to hub 1105.

The hub 1105 receives the aggregated upstream communications by theintegrated splitter and circulator 1180. At the hub 1105, the aggregateupstream wavelengths may be received by a same optical receiver (e.g.,as optical splitter 1170) since the sensitivity of semiconductorphotodetectors cover a very wide wavelength range. For example, InGaAsphotodiodes may receive optical signals between approximately 900 nm and1670 nm. Integrated splitter and circulator 1180 demultiplex theupstream communications (e.g., the splitter or the alternativewavelength multiplexer may filter upstream communications by wavelength)and direct the upstream communications to the optical receivers 1185.The optical receivers 1185 may be, for example, photodetectors.

The light source 1130 of the fiber node 1110 participates in thegeneration of a unique seed source 1150 for each end device 1125. Aspreviously discussed, a comb generator may also be used to generate aseed source for each end device. In FIG. 11, in order to provide theunique seed sources 1150, the fiber node may filter a broad band signal1135 to obtain more than one narrower bandwidth signals where each ofthe narrower bandwidth signals correspond to a unique seed source 1150.The light source 1130 may generate the broadband signal 1135. The lightsource 1130 may be, for example, a super-luminescent light emittingdiode (S-LED), an optical amplifier, a light emitting diode (LED)coupled with an optical amplifier, any appropriate light source thatgenerates a broadband signal, or any combination thereof. The broadbandsignal 1135 may span a large wavelength range. For example, thebroadband signal 1135 may generally span 100 s of nanometers. Forexample, the broadband signal 1135 may span approximately 800 nm to 900nm, 1250 nm to 1350 nm, or 1500 nm to 1600 nm. In some other cases, thebroadband signal 1135 may span wavelengths greater than 1600 nm and/orless than 800 nm.

Filter 1140 may collect the broadband signal 1135 from the light source1130 and filter the broadband signal 1135 to provide the unique seedsources 1150. The filter 1140 may be a wavelength division multiplexing(WDM) filter. For example, the filter 1140 may be an arrayed waveguidegrating filter, a thin film filter or any other appropriate filter orcombination thereof. The filter 1140 may output a plurality of signals1145 that correspond to narrow wavelength slices of the broadband signal1135. The gain curve of broadband signal 1135 (e.g., a shape ofbroadband signal 1135 corresponding to a power for the wavelengthsincluded within broadband signal 1135) and the plurality of signals 1145may be similar. The plurality of signals 1145 includes a summation ofeach of the individual seed sources 1150 being output from filter 1140.The number of seed sources generated by filter 1140 may correspond to anumber of end devices 1125 (e.g., a size of the optical service domaingroup). In some cases, service groups of 40 would match wavelengthfilter sizes designed for DWDM C-band. Nevertheless differentgranularity of wavelength filters and number of ports may be used.Multiple of these 40 port subscriber units can be used in paralleldepending on the total number of subscribers served through the opticalnode.

Each of the seed sources 1150 may include a signal of a narrowerbandwidth (e.g., when compared to a bandwidth of the broadband signal1135). For example, each seed source 1150 may span between 50 gigahertz(GHz) and 100 GHz. In some cases, the center frequency of each of theseed sources 1150 may be offset by 100 GHz. For example, if a first seedsource 1150-a has a center frequency of 191,000 GHz, a neighboring seedsource 1150 (e.g., a seed source corresponding to a next-highest ornext-lowest center frequency) may have a center frequency of 191,100GHz. Other center frequencies may be appropriate such as approximately350,000 GHz, with a neighboring seed source with a center frequency of350,100 GHz. The seed sources 1150 may be directed to a correspondingoptical circulator 1155. The circulator may then direct the seed sourceto a corresponding end device 1125. For example, optical circulator1155-a may direct seed source 1150-a to end device 1125-a by opticalfiber 1120-a. Similarly, optical circulators 1155-b and 1155-c may routeseed sources 1150-b and 1150-c to end devices 1125-b and 1125-crespectively.

The seed sources 1150 may be used for injection locking at the enddevices 1125. Each end device 1125 may include an upstream laser diode.In some cases, each end device 1125 may include a generic laser diode. Ageneric laser diode may include a non-wavelength specific laser diode(e.g., end device 1125-b may include a similar laser diode to end device1125-c). A non-wavelength specific laser diode may be a laser diode withmulti-longitudinal modes that enables injection locking on one of itslongitudal modes overlapping in frequency or in close frequencyproximity of the seed source. In some examples, the end devices maysupport DWDM but may not use wavelength specific structures. The laserdiodes at the end devices 1125 may be referred to as slave lasersources. The seed sources 1150 may function as a substantially-narrowband or single longitudinal mode master to keep the frequency of aresonator mode of the laser diode at the end devices 1125 close enoughto the frequency of the seed source 1150. The end devices 1125 may beconfigured to receive a seed source 1150 input and output a data streamincluding primarily a bandwidth corresponding to the seed source 1150.By injection locking the laser diodes at the end devices 1125, thesystem 1100 may eliminate (or substantially decrease) OBI within thesystem. That is, the end devices 1125 may use a conventional simplecavity (e.g., Fabry Perot) laser diode which, through the filteredwavelength window controlling the seed source injection locking,generate a wavelength that is separated by large frequency gaps from anyother laser diode (and corresponding end device 1125) in the opticalservice domain group. These frequency gaps are large enough such that nooptical beats (mixing products) fall within the frequency response ofthe fiber node 1110.

End devices 1125 may modulate the signals from their respective laserdiodes (e.g., that include primarily the wavelengths corresponding totheir associated seed source) with data and communicate upstreamtransmissions to the fiber node 1110. Modulating the signal at enddevices 1125 will be discussed in further detail herein. Signals 1165-a,1165-b, and 1165-c may correspond in frequency to the seed sources1150-a, 1150-b and 1150-c respectively. Thus, the filter 1140 mayprovide seed sources that may be within certain filtered wavelengthwindows and the corresponding upstream transmissions (e.g., generated atthe end devices 1125) may also be substantially within the filteredwavelength windows and therefore may not cause OBI. The signals 1165 maybe received at an optical circulator 1155 and directed to the opticalsplitter 1170. Signal 1175 illustrates the output from the opticalsplitter 1170. Specifically, each of the signals from the end devices1125 may be aggregated such that signal 1175 is directed to the hub1105.

FIG. 12 is a schematic illustration of a fiber communication system 1200that supports network communication systems and methods in accordancewith an embodiment of the present disclosure. The system 1200 mayinclude one or more components as described with reference to FIGS. 10and 11. For example, the system 1200 may include a hub 1205 incommunication with a fiber node 1210. The hub 1205 and fiber node 1210may be example of hubs 1005 and 1105 and fiber nodes 1010 and 1110 asdescribed with reference to FIGS. 10 and 11, respectively. Further, thesystem 1200 may include end devices 1225 which may be examples of enddevices 1025 and 1125 as described with reference to FIGS. 10 and 11.The end devices 1225 may be user devices which may be capable of havingupstream and downstream capabilities, base stations (e.g., such as basestation 1030 as described with reference to FIG. 10), or other fibernodes 1210. System 1200 may be a PON and, in some cases, may reduceand/or eliminate OBI.

In operation, fiber node 1210 may perform the same general functions asfiber node 1010-a as described with reference to FIG. 10 and fiber node1110 as described with reference to FIG. 11. Fiber node 1210 may directdownstream communications from hub 1205 to end devices 1225 and upstreamcommunications from end devices 1225 to the hub 1205. Fiber node 1210may collect downstream communications from hub 1205. Hub 1205 may directdownstream communications by laser diodes 1235. The downstreamcommunications generated by laser diodes 1235 at the hub 1205 may eachcorrespond to a single end device in the case of a point to pointcommunication (e.g., laser diode 1235-a may generate downstreamcommunications for end device 1225-a) or correspond to multiple enddevices in the case of point to multi-point communication. Thedownstream communications may be collected by the optical splitter andcombiner 1260. The optical splitter and combiner may aggregate thedownstream communications and direct the aggregated downstreamcommunication to optical circulator 1255-e. The optical circulator1255-e may direct the aggregated downstream communication to the fibernode 1210.

The optical circulator 1255-d at the fiber node 1210 may direct theaggregated downstream communication to downstream director 1290. Thedownstream director 1290 may be an optical splitter, or a wavelengthmultiplexer, or a wavelength switch or a combination thereof. In someexamples, the downstream director 1290 may be an optical splitter, andthe downstream director 1290 may direct the aggregated downstreamcommunication to each of the end devices 1225. If the downstreamdirector 1290 is an optical splitter, the downstream traffic 1295-a,1295-b, and 1295-c may include the same aggregated downstreamcommunication each including a same broad wavelength establishing pointto multi-point communications. In some examples, the downstream director1290 may be a wavelength switch, and the downstream director 1290 mayfilter the aggregated downstream signal and output unique downstreamsignals to each end device 1225 establishing point to pointcommunications. Here, optical signals carrying downstream traffic1295-a, 1295-b, and 1295-c may include different wavelengths (e.g.,specific to the end device 1225).

For upstream communications, the fiber node 1210 may provide a uniqueseed source for each end device 1225. As discussed with reference toFIG. 11, the light source 1230 may generate a broadband signal and thefilter 1240-a may output a plurality of seed sources that correspond tonarrow wavelength slices of the broadband signal. In some cases, thelight source 1230 and the filter 1240-a may include a coherent lightsource. Coherent light sources and the corresponding systems and devicesmay be further discussed in U.S. patent application Ser. No. 15/283,632,which is herein incorporated by reference in its entirety. In somecases, the light source 1230 and the filter 1240-a may be replaced bymultiple coherent light sources, which may each generate a uniquecoherent seed source intended for each end device 1225. In some othercases, the light source 1230 may include multiple coherent light sourceswhich may each generate different wavelengths of light, such that thelight source 1230 may generate more than one band of coherent light. Thefilter 1240-a may be configured to separate the bands of coherent lightinto individual seed sources. The seed sources and the optical signalwith downstream data 1295 may be aggregated using an optical coupler1296 (or an optical combiner 1296) prior to being directed to an opticalcirculator 1255. The optical circulator 1255 may direct the seed sourceand downstream data to a corresponding end device 1225. The end devicesmay collect the seed source and the downstream data.

The seed sources may be used for injection locking at the end devices1225. The end devices 1225 may be configured to collect a seed sourceinput and output a data stream including primarily a bandwidthcorresponding to the seed source. By injection locking the laser diodesat the end devices 1225, the system 1200 may avoid (or substantiallydecrease) OBI within the system. End devices 1225 may modulate thesignals at their respective laser diodes (e.g., that include primarilythe wavelengths corresponding to their associated seed source) with dataand communicate upstream transmissions to the fiber node 1210. In someexamples, the end devices 1225 may use external intensity modulationand/or coherent modulation to output the data stream. Thus, the filter1240-a may provide seed sources that exist within certain filteredwavelength windows and the corresponding upstream transmissions (e.g.,generated at the end devices 1225) may also exist within thenon-overlapping filtered wavelength windows and therefore do not causeOBI.

Fiber node 1210 may collect upstream communications from end devices1225 (e.g., by optical fibers 1220). Optical circulators 1255 may directthe upstream communications to the optical splitter 1270. The opticalsplitter 1270 may aggregate the upstream communications. In some cases,the optical splitter 1270 may instead be a wavelength multiplexer Fibernode 1210 may direct the aggregated upstream communication by opticalfiber 1215 to hub 1205 (e.g., through optical circulator 1255-d). Theoptical circulator 1255-e may collect the aggregated upstreamcommunication and direct the aggregated upstream communication to thefilter 1240-b. Filter 1240-b may filter the aggregated upstreamcommunication (e.g., based on wavelength) and direct the filteredupstream communications to receivers 1285. Each receiver 1285 maycollect upstream communication from a single end device 1225. Forexample, receiver 1285-a may collect upstream communications from enddevice 1225-a. Here, receiver 1285-a may collect a filtered upstreamcommunication corresponding to a wavelength range similar to the seedsource collected by end device 1225-a. Alternatively, receivers 1285 maycollect filtered upstream communications from multiple end devices 1225.

FIG. 13A is a schematic illustration of a fiber communications system1300-a that supports network communication systems and methods inaccordance with an embodiment of the present disclosure. The fibercommunication systems 1300-a may include one or more components asdescribed with reference to FIGS. 10 through 12. For example, the enddevice 1325-a may be an example of end devices 1025, 1125, and 1225 asdescribed with reference to FIGS. 10 through 12. End device 1325-a mayinclude a filter 1305-a, optical circulators 1355-a and 1355-b, aphotodetector 1310-a, a laser diode 1315-a, and an external modulator1330-a.

In some examples, the end device 1325-a may include components which maybe integrated together (e.g., integrated within a same end device1325-a) by employing compatible materials for each of the components. Insome examples, the laser diode 1315-a may be an indium phosphide laserdiode and the optical circulators 1355-a and 1355-b may additionally bebased on indium phosphide. In some cases, the indium phosphide laserdiode 1315-a may be integrated together with the external modulator1330-a by employing compatible materials which may be based on thecorresponding material band gaps. In some examples, the indium phosphidelaser diode 1315-a may be integrated with an indium phosphideMach-Zehnder external modulator 1330-a and, the photodetector 1310-a maybe an indium gallium arsenide phosphide photodetector.

End device 1325-a may be in communication with a fiber node (notillustrated in FIG. 13A) by optical fiber 1320-a. The end device 1305-amay collect communications at filter 1305-a. The filter 1305-a may be awaveguide grating filter. In some cases, the filter 1305-a may be astatic filter. For example, the filter 1305-a may be staticallyconfigured to select and direct signals of certain wavelengths. In othercases, the filter 1305-b may be an active filter and the selectedwavelength ranges and/or resulting direction may be configurable. InFIG. 13A, filter 1305-a may be configured to separate and directdownstream communications to the photodetector 1310-a. The downstreamcommunications may include a broad wavelength range (e.g., directed tomore than one end device 1325), and the filter 1305-a may select awavelength range of the downstream communication specific to the enddevice 1325-a and direct this wavelength range to the photodetector.

Additionally, in FIG. 13A, the filter 1305-a may collect communicationsvia optical fiber 1320-a and separate a seed source from the collectedcommunications. The seed source may be directed by the filter 1305-a(e.g., the seed source originating from a fiber node and collected atthe end device) to the optical circulator 1355-a. The seed source may bea signal spanning primarily a wavelength range. In some cases, the seedsource may be generated by a broad spectrum light source. Alternatively,the seed source may be a coherent signal. Coherent signals will bediscussed in further detail herein.

The optical circulator 1355-a may direct the seed source to the secondoptical circulator 1355-b. The second optical circulator 1355-b may bein two-way communication with the laser diode 1315-a. Therefore, thesecond optical circulator 1355-b may direct the seed source upstream andinto the laser diode 1315-a and may direct a signal (e.g., generated bythe laser diode 1315-a) from the laser diode 1315-a downstream to theexternal modulator 1330-a and may direct the seed source signal comingfrom the first circulator to the second circulator to the laser diode.

Laser diode 1315-a may be designed with a cavity length such that atleast one longitudinal mode may correspond to one filtered wavelengthwindow or one tone generated by a comb generator (e.g., 40 or 80 modesor tones). Each mode may correspond to the wavelength range of a signaloutput by the laser diode 1315-a. For example, in a first mode the laserdiode 1315-a may collect a seed source corresponding to a firstwavelength range. Here, the laser diode 1315-a may output a signalincluding primarily the first wavelength range. In a second mode, thelaser diode 1315-a may collect a seed source corresponding to a secondwavelength range (e.g., that is different than the first wavelengthrange). In this example, the laser diode 1315-a may output a differentsignal (e.g., when compared to the first mode) including primarily thesecond wavelength range. The separation between cavity modes may rangefrom tens of GHz to hundreds of GHz.

In some examples, the laser diode 1315-a may be driven by a specificconstant current that results in laser diode 1315-a and seed sourcewavelength spectrum overlap and an injection locked condition. Changinga current supply of the laser diode 1315-a at faster rates may result inthe laser diode 1315-a and the seed source losing the locking condition.Maintaining the laser diode 1315-a at a specific stable operatingcurrent condition that tracks in frequency to the seed source emissionsmay result in reliable injection locked operation. in similar changes tothe resulting wavelength. Because the laser diode 1315-a may not bemodulated at high frequencies (e.g., the current driving laser diode1315-a is constant), the laser diode 1315-a may operate in a mode basedon the wavelength range of the seed source rather than the current.

The laser diode 1315-a may include two facets (e.g., a front facet and arear facet) or reflective surfaces at each end of the cavity of thelaser diode 1315-a. The reflectivity of the laser diode 1315-a may becontrolled to increase an amount of energy that can be input or outputfrom the cavity. The optical circulator 1355-b may direct the seedsource into a front facet of the laser diode 1315-a. The front facetreflectivity and the length of the laser cavity may be used to regulatethe amount of energy directed into and out of the cavity. The seedsource may be used to injection lock a signal being output from thelaser diode 1315-a. Thus, the signal being directed from the laser diode1315-a to the optical circulator 1355-b may be associated with the samewavelength as the collected seed source.

The external modulator 1330-a may intensity modulate the signalgenerated by the laser diode 1315-a. By intensity modulating the signalgenerated by the laser diode 1315-a, the external modulator 1330-a mayprovide a modulated signal and/or encode a signal with information andcorresponding to an upstream communication. Externally modulating thesignal generated by the laser diode 1315-a may allow the laser diode1315-a to be stable (e.g., driven at the constant current).

In some examples, the seed source may be generated by a broad spectrumlight source, and the external modulator 1330-a may provide a singledata stream via amplitude or intensity modulation. In some examples, theseed source may be generated by a coherent light source, and theexternal modulator 1330-a may implement amplitude and phase modulation(e.g., coherent modulation). In some examples, the external modulator1330-a may be an in-phase quadrature modulator. Continuing the example,the external modulator 1330-a may encode up to four data streams intoone optical signal for concurrent upstream communications. Two streamsencoded in each polarization and each polarization encoded with anin-phase stream and a quadrature stream (e.g., 90° out of phase). Theexternal modulator 1330-a may include four different modulators eachconfigured to collect a signal from the laser diode 1315-a and furtherconfigured to output a phase modulated signal to the optical circulator1355-a. The external modulator 1330-a may utilize one or more phaseshift elements and one or more polarization beam splitters to providefour upstream data streams for concurrent communication. Externalmodulation with coherent light sources will be discussed in furtherdetail herein.

In some examples, the external modulator 1330-a may direct the upstreammodulated signal (or signals in the case of coherent modulation) to theoptical circulator 1355-a. The optical circulator 1355-a may direct themodulated signal to the filter 1305-a. The optical circulator 1355-a maykeep the modulated signal (e.g., the upstream communication) separatefrom the downstream communications. That is, the optical circulator1355-a may direct the seed source downstream to the optical circulator1355-b to prevent the downstream communications (e.g., broadband energy)from traversing to the external modulator 1330-a.

The filter 1305-a may direct the upstream communications (e.g., themodulated signal), by optical fiber 1320-a, to the fiber node. Theupstream communications may primarily include the wavelength range ofthe seed source. By controlling the wavelength range of the upstreamcommunications, the end device 1325-a may provide upstreamcommunications that eliminate OBI (and/or significantly decrease OBI).

FIG. 13B is a schematic illustration of a fiber communications system1300-b that supports network communication systems and methods inaccordance with an embodiment of the present disclosure. The fibercommunications system 1300-b may include one or more components asdescribed with reference to FIGS. 10 through 13A. For example, the enddevice 1325-b may be an example of end devices 1025, 1125, and 1225 asdescribed with reference to FIGS. 10 through 12. In some cases, enddevice 1325-b may include aspects of end device 1325-a. For example,filter 1305-b, optical circulators 1355-c and 1355-d, photodetector1310-b, laser diode 1315-b, and external modulator 1330-b may beexamples of the corresponding components in end device 1325-a.

End device 1325-b may be in communication with a fiber node (notillustrated in FIG. 13B) by optical fiber 1320-b. The end device 1325-bmay be another example configuration of an end device (e.g., in additionto end device 1325-a). Specifically, end device 1325-b may demonstratean alternative location of filter 1305-b. As illustrated in FIG. 13A,filter 1305-a may collect downstream communications and a seed source.Alternatively and as illustrated in FIG. 13B, the optical circulator1355-c may collect and direct the downstream communications and the seedsource to the filter 1305-b. In some cases, the filter 1305-a mayintroduce reflection (e.g., towards the fiber node by optical cable1320-a). By placing the filter between optical circulators 1355, the enddevice 1325-b may reduce this undesirable reflection.

The filter 1305-b may separate and direct downstream communications tothe photodetector 1310-b. The filter 1305-b may further separate anddirect a seed source (e.g., from a fiber node) to the optical circulator1355-d. The optical circulator 1355-d may be in two-way communicationwith the laser diode 1315-b. Therefore, the optical circulator 1355-dmay direct the seed source to the laser diode 1315-b and direct a signalgenerated by the laser diode 1315-b and from the laser diode 1315-b tothe external modulator 1330-b. The optical circulator 1355-d may directthe seed source into a front facet of the laser diode 1315-b. The seedsource may be used to injection lock the laser diode 1310-b to generatea signal. Thus, the signal being directed from the laser diode 1310-b tothe optical circulator 1355-d may be associated with the same wavelengthas the seed source.

The external modulator 1330-b may intensity modulate the signalgenerated by the laser diode 1315-b. By intensity modulating the signalgenerated by the laser diode 1315-b, the external modulator 1330-b mayprovide a signal and/or encode information on the signal which maycorrespond to an upstream communication. The external modulator 1330-bmay direct the upstream communication to the optical circulator 1355-c.The optical circulator 1355-c may in turn direct the upstreamcommunication, by optical fiber 1320-b, to the fiber node. The upstreamcommunications may be a modulated signal encoded with information andmay primarily include the wavelength range of the seed source. Bycontrolling the wavelength range of the upstream communications, the enddevice 1325-b may provide upstream communications that eliminate OBI (orsignificantly decrease OBI).

FIG. 13C is a schematic illustration of a fiber communications system1300-c that supports network communication systems and methods inaccordance with an embodiment of the present disclosure. The fibercommunications system 1300-c may include one or more components asdescribed with reference to FIGS. 10 through 13B. For example, the enddevice 1325-c may be an example of end devices 1025, 1125, and 1225 asdescribed with reference to FIGS. 10 through 12. In some cases, enddevice 1325-c may include aspects of end devices 1325-a or 1325-b. Forexample, filter 1305-c, optical circulators 1355-e and 1355-f,photodetectors 1310-c and 1310-d, laser diode 1315-c, and externalmodulator 1330-c may be examples of the corresponding components in enddevice 1325-a.

The end device 1325-c may be another example configuration of an enddevice (e.g., in addition to end devices 1325-a and 1325-b).Specifically, end device 1325-c may demonstrate stimulating the laserdiode 1315-c by rear-facet injection.

End device 1325-c may be in communication with a fiber node (notillustrated in FIG. 13c ) by optical fiber 1320-c. Filter 1305-c may beconfigured to separate and direct downstream communications to thephotodetector 1310-c. The filter 1305-c may further separate and directa seed source (e.g., from a fiber node) to the optical circulator1355-e. The optical circulator 1355-e may direct the seed source to thesecond optical circulator 1355-f. The second optical circulator 1355-fmay be in one-way communication with photodetector 1310-d and two-waycommunication with the laser diode 1315-c.

The second optical circulator 1355-f may direct the seed source to therear facet of the laser diode 1315-c. The rear facet of the laser diode1315-b may direct and/or reflect the signal from the laser diode 1315-bto the optical circulator 1355-f. Thus the signal may be the reflectedsignal from the rear facet of laser diode 1315-c. In some cases, thesignal may include a signal emitted from the rear facet of the laserdiode 1315-c. The optical circulator 1355-f may direct thereflected/emitted signal to photodetector 1310-d. The photodetector1310-d may determine a status and/or health of the light sources and/orlaser diodes located at the end device, based on the signal detected atthe photodetector monitor 1310-d and from the laser diode 1315-c. Forexample, the photodetector monitor 1310-d may detect a wavelengthcomposition of the signal and/or an energy of the signal, or maydetermine an expected energy of the signal. If the detected energy ofthe signal is different than the expected energy of the signal, thephotodetector 1310-d may determine that the light sources of the enddevice may not be operating as expected.

The seed source may be used to injection lock a signal being output fromthe laser diode 1315-c. Thus, the laser diode 1315-c may generate asignal associated with approximately the same wavelength as the seedsource. Because some of the signal may be lost (e.g., by reflection atthe rear facet of the laser diode 1315-c), the gain of the laser diode1315-c in this configuration may be lower than in other configurations.For example, the laser diode 1315-c may have a gain of 40 when usingfront facet injection. However, when using the rear facet injection, thelaser diode 1315-c gain may be in the approximate range of 10 to 40(e.g., depending on the energy of the signal reflected at the rear facetof the laser diode 1315-c to the photodetector 1355-d). The laser diode1315-c may direct the generated signal (e.g., the injection-lockedsignal) from a front facet to the external modulator 1330-c.

The external modulator 1330-c may intensity modulate the signalgenerated by the laser diode 1315-c. By intensity modulating the signalgenerated by the laser diode 1315-c, the external modulator 1330-c mayprovide a modulated signal and/or encode information on a signal,corresponding to an upstream communication. The external modulator1330-c may direct the upstream communication to the optical circulator1355-e which may direct the upstream communication to the filter 1305-c.The filter 1305-c may in turn direct the upstream communication, byoptical fiber 1320-c, to the fiber node. The upstream communications mayprimarily include the wavelength range of the seed source. Bycontrolling the wavelength range of the upstream communications, the enddevice 1325-c may provide upstream communications that eliminate OBI (orsignificantly decrease OBI).

FIG. 14A is a schematic illustration of a fiber communications system1400-a that supports network communication systems and methods inaccordance with an embodiment of the present disclosure. The fibercommunications system 1400-a may include one or more components asdescribed with reference to FIGS. 10 through 13. For example, theexternal modulator 1430-a may be an example of external modulators 1330as discussed with reference to FIG. 13. The external modulator 1430-amay include a phase shift element 1410-a and modulators 1415-a and1415-b.

The external modulator 1430-a may be in upstream communication with alaser diode (not illustrated in FIG. 14A). The laser diode may direct asignal to the external modulator 1430-a. The signal may be a coherentsignal with a frequency corresponding to a seed source. The signal1405-a may be directed to both modulator 1415-a and phase shift element1410-a. The phase shift element 1410-a may introduce a 90° phase shiftto the signal 1405-a and output the phase-shifted signal to modulator1415-b. Therefore, the signal directed to modulator 1415-a may be 90°out of phase with the signal directed to modulator 1415-b. The 90° phaseshift of the phase shift element 1410-a is used for explanatory purposesonly and may be any appropriate phase shift. Modulator 1415-a maymodulate the signal 1405-a to output a first data stream and modulator1415-b may modulate the phase-shifted signal to output a second datastream. The first and second signal streams may be output concurrentlyas upstream signal 1420-a. The upstream communication 1420 a may includetwo distinct data streams being communicated according to a wavelengthcorresponding to the wavelength of a coherent seed source. Therefore,the data streams may not be subject to OBI.

FIG. 14B is a schematic illustration of a fiber communications system1400-b that supports network communication systems and methods inaccordance with an embodiment of the present disclosure. The fibercommunications system 1400-b may include one or more components asdescribed with reference to FIGS. 10 through 13. In some cases, externalmodulator 1430-b may include aspects of external modulator 1430-a. Forexample, phase shift elements 1410-b and 1410-c and modulators 1415-c,1415-d, 1415-e, and 1415-f may be examples of the correspondingcomponents in external modulator 1430-a. The external modulator 1440-bmay further include polarization beam splitter 1425 and polarizationcombiner 1435.

The external modulator 1430-b may be in communication with a laser diode(not illustrated in FIG. 14B). The laser diode may direct a signal tothe external modulator 1430-b. The signal may be a coherent signal witha frequency corresponding to a seed source. The external modulator1430-b may utilize phase shift element 1410-b and 1410-c andpolarization beam splitter 1425 to provide four separately modulatedsignals with unique combinations of polarization and phase shifts, whichmay be suitable for concurrent upstream communication.

The signal 1405-b may be directed to polarization beam splitter 1425.The polarization beam splitter 1425 may split signal 1405-b into a firstpolarization signal and a second polarization signal in which the firstand second polarization signals may be different polarizations. Forexample, polarization beam splitter 1425 may provide a firstpolarization signal to a phase shift element 1410-b and modulator 1415-dand provide a second polarization signal to phase shift element 1410-cand modulator 1415-f. The phase shift elements 1410-b and 1410-c mayintroduce a 90° phase shift to the signal collected from thepolarization beam splitter 1425. The phase shift element 1410-b mayoutput the phase-shifted signal to modulator 1415-c and the phase shiftelement 1410-c may output the phase-shifted signal to modulator 1415-e.

Thus, between the phase shift elements 1410-b and 1410-c and thepolarization beam splitter 1425, each of the signals collected by themodulators 1415-c, 1415-d, 1415-e, and 1415-f may have a uniquecombination of polarization and phase shift, which may be suitable forconcurrent upstream communication. The modulators 1415-c, 1415-d,1415-e, and 1415-f may modulate the collected signals and output a datastream to the polarization combiner 1435. The polarization combiner 1435may combine each of the data streams and output upstream communication1420-b. The upstream communication 1420-b may include four distinct datastreams being communicated according to a wavelength corresponding tothe wavelength of a coherent seed source. Therefore, the data streamsmay not be subject to OBI.

FIG. 15 shows a process flow 1500 that supports network communicationsystems and methods in accordance with aspects of the presentdisclosure. The process flow 1500 may include operations performed by afiber node 1505, which may be an example of a fiber node or a componentof a fiber node as described with reference to FIGS. 10 through 14. Theprocess flow may further include operations performed by an end device1510 which may be an example of an end device or a component of an enddevice as described with reference to FIGS. 10 through 14.

At 1515, the fiber node 1505 may generate, by a light source, a broadwavelength spectrum with a first wavelength range.

At 1520, the fiber node 1505 may collect, at an optical filter, thebroad wavelength spectrum with the first wavelength range.

At 1525, the fiber node 1505 may provide, by the optical filter, a seedsource from the broad wavelength spectrum. The seed source may include asecond wavelength range that is narrower than the first wavelengthrange. The seed source may to be directed to a laser diode (e.g., at theend device 1510) to stimulate the laser diode to emit an optical signal.In some cases, the fiber node 1505 may provide more than one seed sourcefrom the broad wavelength spectrum. For example, the fiber node 1505 mayprovide, by the optical filter, a second seed source from the firstwavelength range, where the second seed source includes a thirdwavelength range narrower than the first wavelength range and differentthan the second wavelength range.

At 1530, the fiber node 1505 may output the seed source to the enddevice 1510.

At 1535, the end device may collect a seed source spanning a wavelengthrange (e.g., the second wavelength range). In some cases, collecting theseed source may include filtering, at the end device, a combined signalto separately direct a downstream signal and the seed source. The enddevice may communicate the downstream signal to a photodetector and theseed source to the laser diode.

At 1540, the seed source may generate a signal including primarily thewavelength range (e.g., the second wavelength range) by stimulating alaser diode using the seed source. In some cases, stimulating the laserdiode may include injection locking the laser diode using the seedsource.

At 1545, the end device may modulate the signal including primarily thewavelength range (e.g., the second wavelength range). The end device maymodulate the signal by externally modulating the signal or intensitymodulating the signal at the laser diode.

At 1550, the end device may output the modulated signal (e.g., includingprimarily the second wavelength range). The fiber node 1505 may collect,at an optical splitter, the modulated signal. The modulated signal(e.g., as collected by the optical splitter) may be externally modulatedand/or intensity modulated.

FIG. 16 shows a block diagram 1600 that supports network communicationsystems and methods of a fiber node 1605 in accordance with aspects ofthe present disclosure. The device 1605 may be an example of aspects ofa fiber node and an optical hub as described with reference to FIGS. 1through 15. The fiber node 1605 may include a broad wavelength spectrumgenerator 1610, a broad wavelength spectrum collector 1615, a seedsource generator 1620, and a signal collector 1625. Each of thesemodules may communicate, directly or indirectly, with one another (e.g.,via one or more buses, fibers, cables, wires, and so forth).

The broad wavelength spectrum generator 1610 may generate, by a lightsource, a broad wavelength spectrum with a first wavelength range.

The broad wavelength spectrum collector 1615 may collect, at an opticalfilter, the broad wavelength spectrum with the first wavelength range.

The seed source provider 1620 may provide, by the optical filter, a seedsource from the broad wavelength spectrum, the seed source to bedirected to a laser diode to stimulate the laser diode to emit anoptical signal, where the seed source includes a second wavelength rangenarrower than the first wavelength range. In some examples, providing,by the optical filter, a second seed source from the first wavelengthrange, where the second seed source includes a third wavelength rangenarrower than the first wavelength range and different than the secondwavelength range. In some cases, stimulating the laser diode to emit anoptical signal further includes injection locking the laser diode usingthe seed source.

The signal collector 1625 may collect, at an optical splitter,externally modulated upstream signals, where the externally modulatedupstream signals include primarily the second wavelength range. In someexamples, the signal collector 1625 may collect, at an optical splitter,intensity modulated upstream signals, where the intensity modulatedupstream signals include primarily the second wavelength range.

FIG. 17 shows a block diagram 1700 that supports network communicationsystems and methods of an end device 1705 in accordance with aspects ofthe present disclosure. The end device 1705 may be an example of aspectsof an end device as described with reference to FIGS. 1 through 9 or anend device as described with reference to FIGS. 10 through 16. The enddevice 1705 may include a seed source collector 1710, a signal generator1715, a signal modulator 1720, and a signal outputter 1725. Each ofthese modules may communicate, directly or indirectly, with one another(e.g., via one or more buses, fibers, cables, wires, and so forth).

The seed source collector 1710 may collect a seed source spanning awavelength range. The seed source collector 1710 may collect the seedsource at an optical splitter. In some examples, the seed sourcecollector 1710 may filter a combined signal to separately direct adownstream signal and the seed source. In some cases, the seed sourcecollector 1710 may communicate the downstream signal to a photodetectorand the seed source to the laser diode.

The signal generator 1715 may generate a signal including primarily thewavelength range. The signal generator 1715 may generate the signalbased on collecting the seed source (e.g., at the seed source collector1710). In some cases, the signal generator 1715 may generate the signalby stimulating a laser diode using the seed source. In some examples,generating the signal further includes injection locking the laser diodeusing the seed source. The signal generator 1715 may drive the laserdiode at a constant current.

The signal modulator 1720 may modulate the signal including primarilythe wavelength range. In some examples, modulating the signal furtherincludes externally modulating the signal. In some cases, modulating thesignal further includes intensity modulating the signal at the laserdiode. The signal modulator 1720 may modulate the signal based on one ormore data streams.

The signal outputter 1725 may output the modulated signal. The signaloutputter 1725 may output the modulated signal by the opticalcirculator.

FIG. 18 shows a flow chart illustrating a method 1800 that supportsnetwork communication systems in accordance with aspects of the presentdisclosure. The operations of method 1800 may be implemented by a fibernode or its components as described herein. For example, the operationsof method 1800 may be performed by a fiber node as described withreference to FIG. 16. In some examples, a fiber node may execute a setof instructions to control the functional elements of the fiber node andto perform the described functions. Additionally or alternatively, thefiber node may perform aspects of the described functions usingspecial-purpose hardware.

At 1805, the fiber node may generate, by a light source, a broadwavelength spectrum with a first wavelength range. The operations of1805 may be performed according to the methods described herein. In someexamples, aspects of the operations of 1805 may be performed by a broadwavelength spectrum generator as described with reference to FIG. 16.

At 1810, the fiber node may collect, at an optical filter, the broadwavelength spectrum with the first wavelength range. The operations of1810 may be performed according to the methods described herein. In someexamples, aspects of the operations of 1810 may be performed by a broadwavelength spectrum collector as described with reference to FIG. 16.

At 1815, the fiber node may provide, by the optical filter, a seedsource from the broad wavelength spectrum, the seed source to bedirected to a laser diode to stimulate the laser diode to emit anoptical signal, where the seed source includes a second wavelength rangenarrower than the first wavelength range. The operations of 1815 may beperformed according to the methods described herein. In some examples,aspects of the operations of 1815 may be performed by a seed sourceprovider as described with reference to FIG. 16.

FIG. 19 shows a flow chart illustrating a method 1900 that supportsnetwork communication systems in accordance with aspects of the presentdisclosure. The operations of method 1900 may be implemented by a fibernode or its components as described herein. For example, the operationsof method 1900 may be performed by a fiber node as described withreference to FIG. 16. In some examples, a fiber node may execute a setof instructions to control the functional elements of the fiber node toperform the described functions. Additionally or alternatively, a fibernode may perform aspects of the described functions usingspecial-purpose hardware.

At 1905, the fiber node may generate, by a light source, a broadwavelength spectrum with a first wavelength range. The operations of1905 may be performed according to the methods described herein. In someexamples, aspects of the operations of 1905 may be performed by a broadwavelength spectrum generator as described with reference to FIG. 16.

At 1910, the fiber node may collect, at an optical filter, the broadwavelength spectrum with the first wavelength range. The operations of1910 may be performed according to the methods described herein. In someexamples, aspects of the operations of 1910 may be performed by a broadwavelength spectrum collector as described with reference to FIG. 16.

At 1915, the fiber node may provide, by the optical filter, a seedsource from the broad wavelength spectrum, the seed source to bedirected to a laser diode to stimulate the laser diode to emit anoptical signal, where the seed source includes a second wavelength rangenarrower than the first wavelength range. In some cases, stimulating thelaser diode to emit the optical signal may include injection locking thelaser diode using the seed source. The operations of 1915 may beperformed according to the methods described herein. In some examples,aspects of the operations of 1915 may be performed by a seed sourceprovider as described with reference to FIG. 16.

At 1920, the fiber node may provide, by the optical filter, a secondseed source from the first wavelength range, where the second seedsource includes a third wavelength range narrower than the firstwavelength range and different than the second wavelength range. Theoperations of 1920 may be performed according to the methods describedherein. In some examples, aspects of the operations of 1920 may beperformed by a seed source provider as described with reference to FIG.16.

FIG. 20 shows a flow chart illustrating a method 2000 that supportsnetwork communication systems in accordance with aspects of the presentdisclosure. The operations of method 2000 may be implemented by an enddevice or its components as described herein. For example, theoperations of method 2000 may be performed by an end device as describedwith reference to FIG. 17. In some examples, an end device may execute aset of instructions to control the functional elements of the end deviceto perform the described functions. Additionally or alternatively, anend device may perform aspects of the described functions usingspecial-purpose hardware.

At 2005, the end device may collect a seed source spanning a wavelengthrange. The operations of 2005 may be performed according to the methodsdescribed herein. In some examples, aspects of the operations of 2005may be performed by a seed source collector as described with referenceto FIG. 17.

At 2010, the end device may generate a signal including primarily thewavelength range by stimulating a laser diode using the seed source. Theoperations of 2010 may be performed according to the methods describedherein. In some examples, aspects of the operations of 2010 may beperformed by a signal generator as described with reference to FIG. 17.

At 2015, the end device may modulate the signal including primarily thewavelength range. The operations of 2015 may be performed according tothe methods described herein. In some examples, aspects of theoperations of 2015 may be performed by a signal modulator as describedwith reference to FIG. 17.

At 2020, the end device may output the modulated signal. The operationsof 2020 may be performed according to the methods described herein. Insome examples, aspects of the operations of 2020 may be performed by asignal outputter as described with reference to FIG. 17.

FIG. 21 shows a flow chart illustrating a method 2100 that supportsnetwork communication systems in accordance with aspects of the presentdisclosure. The operations of method or methods 2100 may be implementedby an end device or its components as described herein. For example, theoperations of method 2100 may be performed by an end device as describedwith reference to FIG. 17. In some examples, an end device may execute aset of instructions to control the functional elements of the end deviceto perform the described functions. Additionally or alternatively, anend device may perform aspects of the described functions usingspecial-purpose hardware.

At 2105, the end device may collect a seed source spanning a wavelengthrange. The operations of 2105 may be performed according to the methodsdescribed herein. In some examples, aspects of the operations of 2105may be performed by a seed source collector as described with referenceto FIG. 17.

At 2110, the end device may generate a signal including primarily thewavelength range by injection locking a laser diode using the seedsource. The operations of 2110 may be performed according to the methodsdescribed herein. In some examples, aspects of the operations of 2110may be performed by a signal generator as described with reference toFIG. 17.

At 2115, the end device may externally modulate the signal includingprimarily the wavelength range. The operations of 2115 may be performedaccording to the methods described herein. In some examples, aspects ofthe operations of 2115 may be performed by a signal modulator asdescribed with reference to FIG. 17.

At 2120, the end device may output the modulated signal. The operationsof 2120 may be performed according to the methods described herein. Insome examples, aspects of the operations of 2120 may be performed by asignal outputter as described with reference to FIG. 17.

FIG. 22 shows a flow chart illustrating a method 2100 that supportsnetwork communication systems in accordance with aspects of the presentdisclosure. The operations of method or methods 2100 may be implementedby an end device or its components as described herein. For example, theoperations of method 2100 may be performed by an end device as describedwith reference to FIG. 17. In some examples, an end device may execute aset of instructions to control the functional elements of the end deviceto perform the described functions. Additionally or alternatively, anend device may perform aspects of the described functions usingspecial-purpose hardware.

At 2105, the end device may collect, at an optical circulator, a seedsource spanning a wavelength range. The operations of 2105 may beperformed according to the methods described herein. In some examples,aspects of the operations of 2105 may be performed by a seed sourcecollector as described with reference to FIG. 17.

At 2110, the end device may generate a signal including primarily thewavelength range based on collecting the seed source. The operations of2110 may be performed according to the methods described herein. In someexamples, aspects of the operations of 2110 may be performed by a seedsource collector as described with reference to FIG. 17.

At 2115, the end device may externally modulate the signal includingprimarily the wavelength range. The operations of 2115 may be performedaccording to the methods described herein. In some examples, aspects ofthe operations of 2115 may be performed by a seed source collector asdescribed with reference to FIG. 17.

At 2120, the end device may output, by the optical circulator, themodulated signal. The operations of 2120 may be performed according tothe methods described herein. In some examples, aspects of theoperations of 2120 may be performed by a seed source collector asdescribed with reference to FIG. 17.

It should be noted that the methods described herein describe possibleimplementations, and that the operations and the steps may be rearrangedor otherwise modified and that other implementations are possible.Further, aspects from two or more of the methods may be combined.

As illustrated in the embodiments described herein, a difference betweenupstream and downstream signal transmission is that an entiresynchronized modulated/unmodulated channel pair (e.g., second datastream pair 702, FIG. 7) can be transmitted in the downstream direction,whereas, in the upstream direction, only a data modulated signal (e.g.,upstream modulated data stream 176 (Ch1′)) to be transmitted over theupstream fiber connection, i.e., upstream fiber 110. An advantage of thepresent configuration is that the LO for upstream coherent collection(e.g., at upstream receiver 132, FIG. 1) comes directly from the splitsignal, i.e., first unmodulated signal 168 (Ch1) generated from opticalfrequency comb generator 114 (or multiple quality lasers spaced apart infrequency) within optical hub 102, after separation by first hub opticaldemultiplexer 124, as depicted in FIG. 1. Conventional systems typicallyrequire LO generation at each stage of the respective system. Accordingto the present disclosure, on the other hand, relatively inexpensiveslave lasers can be implemented throughout the system architecture formodulation and polarization multiplexing in both optical hub 102 and enddevice 106 components, without requiring an additional LO source at theend device.

According to the present disclosure, utilization of dual-polarizationoptical transmitters, and by direct modulation of semiconductor laserswith coherent collection, is particularly beneficial for not onlylong-haul applications, but also for short-reach applications to reducethe cost of electronic hardware, while also rendering the overallnetwork system architecture more compact. The present systems andmethods further solve the conventional problem of synchronizing twolaser sources over a long period of time. Utilization of the phasesynchronized data stream pairs and slave lasers herein allows continualsynchronization of the various laser sources throughout the systemduring its entire operation. These solutions can be implemented withincoherent DWDM-PON system architectures for access networks in acost-efficient manner.

Utilization of the high quality optical comb source at the front end ofthe system thus further allows a plurality of simultaneous narrowbandwidth wavelength channels to be generated with easily controlledspacing, and therefore also simplified tuning of the entire wavelengthcomb. This centralized comb light source in the optical hub providesmaster seeding sources and LO signals that can be reused throughout thesystem, and for both downstream and upstream transmission. Theimplementation of optical injection, as described herein, furtherimproves the performance of low-cost multi-longitudinal slave lasersources in terms of spectral bandwidth and noise properties. Accessnetworks according to the present systems and methods thus achieve moreefficient transmission of wavelengths through optical fibers, therebyincreasing the capacity of transmitted data, but at lower power,increased sensitivity, lower hardware cost, and a reduction indispersion, DSP compensation, and error correction.

Embodiments of fiber communication systems and methods are describedabove in detail. The systems and methods of this disclosure though, arenot limited to only the specific embodiments described herein, butrather, the components and/or steps of their implementation may beutilized independently and separately from other components and/or stepsdescribed herein. Additionally, the embodiments can be implemented andutilized in connection with other access networks utilizing fiber andcoaxial transmission at the end device stage.

This written description uses examples to disclose the embodiments,including the best mode, and also to enable any person skilled in theart to practice the embodiments, including making and using any devicesor systems and performing any incorporated methods. The patentable scopeof the disclosure is defined by the claims, and may include otherexamples that occur to those skilled in the art. Such other examples areintended to be within the scope of the claims if they have structuralelements that do not differ from the literal language of the claims, orif they include equivalent structural elements with insubstantialdifferences from the literal language of the claims.

Although specific features of various embodiments of the disclosure maybe shown in some drawings and not in others, this is for convenienceonly. In accordance with the principles of the disclosure, a particularfeature shown in a drawing may be referenced and/or claimed incombination with features of the other drawings. For example, thefollowing list of example claims represents only some of the potentialcombinations of elements possible from the systems and methods describedherein.

The functions described herein may be implemented in hardware, softwareexecuted by a processor, firmware, or any combination thereof. Ifimplemented in software executed by a processor, the functions may bestored on or transmitted over as one or more instructions or code on acomputer-readable medium. Other examples and implementations are withinthe scope of the disclosure and appended claims. For example, due to thenature of software, functions described herein can be implemented usingsoftware executed by a processor, hardware, firmware, hardwiring, orcombinations of any of these. Features implementing functions may alsobe physically located at various positions, including being distributedsuch that portions of functions are implemented at different physicallocations.

As used herein, including in the claims, “or” as used in a list of items(e.g., a list of items prefaced by a phrase such as “at least one of” or“one or more of”) indicates an inclusive list such that, for example, alist of at least one of A, B, or C means A or B or C or AB or AC or BCor ABC (i.e., A and B and C). Also, as used herein, the phrase “basedon” shall not be construed as a reference to a closed set of conditions.For example, an exemplary step that is described as “based on conditionA” may be based on both a condition A and a condition B withoutdeparting from the scope of the present disclosure. In other words, asused herein, the phrase “based on” shall be construed in the same manneras the phrase “based at least in part on.”

In the appended figures, similar components or features may have thesame reference label. Further, various components of the same type maybe distinguished by following the reference label by a dash and a secondlabel that distinguishes among the similar components. If just the firstreference label is used in the specification, the description isapplicable to any one of the similar components having the same firstreference label irrespective of the second reference label, or othersubsequent reference label.

The description set forth herein, in connection with the appendeddrawings, describes example configurations and does not represent allthe examples that may be implemented or that are within the scope of theclaims. The term “exemplary” used herein means “serving as an example,instance, or illustration,” and not “preferred” or “advantageous overother examples.” The detailed description includes specific details forthe purpose of providing an understanding of the described techniques.These techniques, however, may be practiced without these specificdetails. In some instances, well-known structures and devices are shownin block diagram form in order to avoid obscuring the concepts of thedescribed examples.

The description herein is provided to enable a person skilled in the artto make or use the disclosure. Various modifications to the disclosurewill be readily apparent to those skilled in the art, and the genericprinciples defined herein may be applied to other variations withoutdeparting from the scope of the disclosure. Thus, the disclosure is notlimited to the examples and designs described herein, but is to beaccorded the broadest scope consistent with the principles and novelfeatures disclosed herein.

What is claimed is:
 1. An apparatus for network communications,comprising: a first optical circulator configured to collect a seedsource spanning a wavelength range and direct the seed source to a laserdiode; the laser diode configured to output a signal comprisingprimarily the wavelength range based at least in part on the collectingthe seed source at the laser diode; an external modulator configured tomodulate the signal output by the laser diode, wherein the first opticalcirculator is further configured to collect the modulated signal anddirect the modulated signal upstream; and a second optical circulatordisposed between the laser diode and the external modulator.
 2. Theapparatus of claim 1, further comprising: a filter configured to:collect the seed source and a downstream signal; separate the seedsource and the downstream signal; and direct the seed source to thefirst optical circulator and the downstream signal to a photodetector.3. The apparatus of claim 1, wherein outputting the signal comprisingprimarily the wavelength range is based at least in part on injectionlocking the laser diode using the seed source.
 4. The apparatus of claim1, wherein the second optical circulator is in one-way communicationwith the external modulator and in two-way communication with the laserdiode.
 5. The apparatus of claim 1, wherein the laser diode furthercomprises: a front facet and the laser diode is further configured tocollect the seed source at the front facet of the laser diode.
 6. Theapparatus of claim 1, wherein the second optical circulator is disposedbetween and in one-way communication with the first optical circulatorand the laser diode.
 7. The apparatus of claim 6, wherein the laserdiode further comprises: a rear facet and the laser diode is configuredto collect the seed source by the rear facet of the laser diode.
 8. Theapparatus of claim 7, further comprising: a photodetector in one-waycommunication with the second optical circulator and configured tocollect a portion of the seed source reflected from the rear facet ofthe laser diode to the photodetector, by the second optical circulator.9. An apparatus for network communications, comprising: a first opticalcirculator configured to collect a combined signal comprising adownstream signal and a seed source spanning a wavelength range; afilter configured to collect the combined signal from the first opticalcirculator and separate the downstream signal and the seed source; alaser diode configured to collect the seed source and output a signalcomprising primarily the wavelength range based at least in part oncollecting the seed source at the laser diode; an external modulatorconfigured to modulate the laser diode signal output, wherein the firstoptical circulator is further configured to collect the modulated signalfrom the external modulator and direct the modulated signal upstream;and a second optical circulator disposed between the laser diode and theexternal modulator and configured to collect the seed source from thefilter, wherein the second optical circulator is in one-waycommunication with the filter and the external modulator and in two-waycommunication with the laser diode.
 10. The apparatus of claim 9,further comprising: a second external modulator disposed between thefirst optical circulator and the second optical circulator, wherein thesecond external modulator is configured to collect the laser diodesignal output from the second optical circulator and further configuredto direct a second externally modulated signal to the first opticalcirculator; and a phase shift element disposed between the externalmodulator and the second optical circulator.
 11. The apparatus of claim10, wherein the seed source is a coherent signal.
 12. The apparatus ofclaim 11, further comprising: a polarization beam splitter disposedbetween the second optical circulator and the phase shift element. 13.The apparatus of claim 12, further comprising: a third externalmodulator disposed between the polarization beam splitter and the firstoptical circulator, wherein the third external modulator is configuredto input a polarized signal from the polarization beam splitter; afourth external modulator; and a second phase shift element disposedbetween the polarization beam splitter and the fourth externalmodulator, wherein the fourth external modulator is configured to inputthe phase shifted signal from the second phase shift element.
 14. Theapparatus of claim 11, further comprising: a polarization combinerdisposed between the first optical circulator and the externalmodulator.
 15. The apparatus of claim 9, wherein the external modulatoris configured to use coherent modulation such that the modulated signalcomprises more than one data stream.
 16. The apparatus of claim 15,wherein the external modulator further comprises an in-phase quadraturemodulator.
 17. The apparatus of claim 9, wherein the laser diode isconfigured to collect any seed source of a plurality of seed sourceseach spanning a unique wavelength range.
 18. The apparatus of claim 9,wherein the filter is further configured to direct the downstream signalto a photodetector.